Roblox cannot enforce deals made between players. This is why we have official trading and sales systems, so that players can make deals and sell items without being scammed. Once you have completed a trade or sale as the result of making a deal with another player, we are not able to reverse it or return your items or currency. If you think a trade is a bad idea, it probably is, and you shouldn't do it.
Examples of such deals include: making deals for items, currency, groups, etc. that are not included in the trade, lending your items or letting a player borrow them, making deals to accept one trade before another and giving your item to someone else to sell or trade.
Please make sure to use the Report Abuse buttons located throughout the site to report anyone who is scamming. It's the best way to help prevent this from happening in the future.
For more information on this and related matters, please see the following pages: