Although Fast Flash scam was prevented when Animal Jam Classic changed trading, it created the Double Accept variant, and is commonly used to scam.
As of February 5th, 2020 in Animal Jam Play Wild, it is no longer possible to do either of these two methods as the new trading system has changed, nullifying these scams in the process.
Flash scams takes two forms of variants, where the scammer's goal is to get the victim's item stolen before their very eyes, leaving the victim unable to realize they have been tricked.
Double Accept (Also known as Anti-Decline or Accept, Accept, Decline) is the method many scammers used in Animal Jam Classic and often used in fake giveaways as well as sometimes combining it with Trust. This is created on January 7th, 2016 in order to exploit the warning system.
You're told to do the first accepting step of a trade, then the next step, but then decline really fast. Meaning, you have to accept, accept, and decline. A scammer will sometimes imply that there's a 3rd confirmation step, sometimes even saying that this scam has no risk, but a 3rd step doesn't exist. After you accept twice, the scammer can easily complete the trade and take your item away from you before locking the den.
Fast Flash (Also known as Original Flash) was the method scammers used to take away the items from their victims. Ever since January 7th, 2016, Fast Flash became the Double Accept method for Animal Jam Classic while Animal Jam Play Wild changed the new trading system entirely on February 5th, 2020.
A scammer will taunt the victim by offering the victim a valuable item for another valuable item for a fair trade, but the scammer will cancel the trade quickly in order to taunt them, claiming they are not fast enough. They'll usually do this a few more times until they swap the valuable item for a storebought item. This creates an illusion where the victim is unable to react in time to realize what is going on until is too late, causing the scammer to steal the valuable item away from the victim.
How to avoid this scam
Double Accept: Don't participate! Although it was originally a party game, it simply isn't anymore. This is a method of scamming, so don't participate in it, even if it's with a buddy. If someone hosts a giveaway like this and it seems legitimate, it's because they're using all the right tricks (returning items, spare accounts, helpers, etc).
Fast Flash: Double check the item to make sure the item you have is the item you want. Make sure you stop and look at the item closely. If the scammer is trying to pull off the trickery, decline the trade.