Limited is a label given to avatar shop items available in finite quantities. They are initially regular items that are sold by Roblox for a set price until they are taken offsale, or in the case of a limited-unique item, until there are no more available copies. When this occurs, they will become limited items, which can be traded or resold for Robux by owners of the item with an active Roblox Premium subscription.
Limited items are classed as 'collectibles' by Roblox, which means that multiple copies of a specific Limited item can be attained and stored in a user's inventory. They are a quintessential part of the trading system, and because of their ability to be traded and resold, they are a very large part of the Roblox economy in general.
The Recent Average Price (or 'RAP') of an item shows the average sale price for the item in question over a recent period in time. This value can fluctuate heavily; for example, one day the Beautiful Hair for Beautiful Space People may have a RAP of over 3,000 Robux, and other days it may drop to lower than 2,500 Robux. A limited item's demand can be determined by monitoring its RAP.
After purchasing or trading for a limited item, users can resell the item for Robux. This feature allows users to sell back unwanted items. Item selling can be done through the item page itself by clicking the dropdown in the top right hand side of the page and then clicking Sell. Only users with an active Roblox Premium subscription can sell items.
When selling items, keep the lowest current price in mind. When looking to get Robux quickly, a limited item is typically sold for lower than the lowest current price. If the item is speculated to raise soon, it can be put on sale at a higher price; then, when the item raises, it will be bought for the higher price.
Limited unique (LimitedU) items are those which are sold in specific quantities with a fixed price upon release and immediately become available for resale or tradable once sold out, compared to limited items which generally go offsale as regular items until they are manually selected to become limited. There are also serial numbers attached to the item depending on when the item was purchased. Limited unique items are often seen as more valuable than regular limited items, and this is amplified by demand for certain serial numbers, which also signify when the unique copy was purchased (#1, #14, #42, #1337, etc.).
The amount of bots (or 'item snipers'), purchasing limited unique items as soon as they come out, or buying up multiple copies of an existing limited at the same time, has caused a large amount of backlash. It is a prominent issue with low-stock items such as the Immortal Swords due to their much higher chance of skyrocketing in value for the owners.
Some issues arose from the release of certain limited items in late 2018 and early 2019. A few examples of these are Horns of the Creature, Torque the Blue Orc and the Wanwood Autumn King Crown. Eventually this resulted in Roblox placing the release of new limited unique items on hold until further notice. The most recent bug, which allowed players to obtain limited items for free while others have already spent Robux on them, has been speculated as one of the main causes of the drought of new limiteds.
It took 9 months since the Noob Assist: Astronaut Action for another new limited to be released in 2019, in the form of the Dominus Formidulosus, which was first purchasable on a timer for a day. After UGC was announced, Roblox noted in a Frequently Asked Question response that UGC creators would be able to make limited items sometime in the future, and that limited and limited unique items made by ROBLOX would return as soon as the issues with them were fixed. 
As of November 10th, 2020, no regular items have gone limited at all since the Black Friday 2019 sale.
In certain times (usually Christmas/Black friday,) Limited items shoot up in price very quickly, and takes long to go down back to its original prices. This is from the higher amounts of Robux being purchased to purchase limiteds. Many traders and players dislike this certain time due to "cheap" items like the Shaggy originally being sold for a reasonable price, but then shooting up to 2-5 times the original price once inflation begins to take effect on the market. (images below for more reference)
Although limited items follow the general rule of supply and demand, many players still dislike this because of instances such as an item being sold for 50 Robux rising to 50,000 in a short span of time. Many players also dislike instances where there are no resellers for an item, making it impossible to get until someone puts a copy on sale. This issue is exacerbated by 'hoarders', a term used to describe users who buy or trade for a high quantity of a specific Limited item in order to take those copies out of circulation with the end goal of increasing the item's value to be resold or traded at a hefty profit.
Another issue arises from price-warring, which begins with two or more users wanting to sell a copy of a limited item, and continuing to lower the price so that their copy is sold first. In large magnitudes, this issue can greatly impact the value and RAP of a limited item, which also hinders others from selling copies at a reasonable price.
As with all online games that have trade systems, there are users who seek illegitimate gains through scamming. Since Roblox introduced trading in 2012, there have been many deceptive tricks that users have employed (such as the infamous 'double-trade' scam) in order to con others out of their limiteds.
In some cases, malicious users may obtain a poisoned limited on purpose, attempt to quickly trade it off to someone else, with the intended result of the recipient being terminated. Users have called on Roblox to be more careful when reviewing these incidents.
Roblox has sometimes removed limited items from terminated players' inventories, even though they are already considered to be deleted forever when the user is initially terminated. This is often for players that use the "One Time Rollback" feature. One known example was ContentCool in 2016; due to Linkmon99 getting compromised several times and ContentCool purchasing his 'stolen' limiteds, almost all of ContentCool's items were taken after his termination.
Since Roblox does not manually resell or redistribute a terminated player's limiteds, they are essentially gone forever, and this has led to concerns from many users because of the effects on the limited economy as well as the site's history.
Users consider an item rare when it has a low stock (usually less than 100 copies in existence). Although some items may sell for a high price, they may not be considered valuable because it has low demand (which is due to the incredibly high price). Due to the low stock, the recent average prices (also known as RAP) may be low, and the item is thus perceived of less value. Rare items are the most expensive items in the catalog and the reason for their low RAP is because hardly any copies of them are ever sold.
A limited with high demand is wanted by a large number of people, which is why many of these items have moderate stocks but are worth considerably more than you would expect. These types of limiteds commonly sell daily and have ascending prices. An item can be high demand mostly when it has a high stock and is bought several times a day.
A limited that is projected is intentionally sold for a very high price while the RAP dramatically rises extremely high. They mostly vary with low stock (around 10,000 or less) and are not sold as much by users. Once a limited is projected, it will start to sell under RAP due to the unexpected price change and rapidly descend to its original selling price and RAP. These limiteds are not as favored by the community and are considered to be 'foul' or 'scamming' items, although some may attempt to take advantage of the price illusion.
LPPing (LPP meaning Lowest Price Possible) is the opposite of projecting, and is usually done in an attempt to lower an item's value. For example, if a limited with 100,000 RAP that had barely sold in the last 30 days was suddenly put up for only 1 Robux and purchased, the RAP would be decreased significantly.
A poisoned item is one that has been stolen from a user's account. These items contain the risk of the owner being banned without awareness. They are not commonly traded around but can be traded for without notice. Bans from harboring a poisoned item can be appealed, but it depends if the owner intentionally or unintentionally traded for the item (often judged by whether they offered lower or higher value in RAP for the item).
- Some users with at least 10 copies or more of the same limited item may spam the "Private Sales" section of the limited item's page, with each copy usually costing the same price.
- When a user purchases a limited item, it will appear next to the last item the user bought after it became a limited item.
- Although users can only purchase one copy of a limited unique item per account while it is still in stock, some have used methods to purchase more than one on the same account. These accounts are usually terminated by Roblox shortly afterward.
- Almost all limited items' prices are slowly increasing over time. (e.g. Super Super Happy Face costed around 30K in October 2020, but in April 2021, it costed an average of 85K.)