A scammer hosts a scam giveaway, and their spare/helper pretends to have been scammed by the host. After that, some people present at the 'giveaway' may believe the spare/helper, and will give them items to "help them recover". They won't know that they just gifted the items to the host's spare or helper.
A scammer hosts a scam giveaway, and their spare/helper pretends to have been scammed by the host. The spare will message a user who was at the 'giveaway', saying that they found the host, and need their help to persuade the host to give the items back.
The spare/helper and the jammer who was messaged will go talk to the host. The host will tell the jammer this: "I'll give the victim's items back if you give me this rare item." If the jammer had been scammed during the 'giveaway', the host may also offer to return their scammed items. The jammer may give the host the item they asked for, not realizing that the "victim" was a spare/helper. The host will never give the jammer their items back.
How to avoid this scam
If you want to give someone something after you think they've gotten scammed, that's perfectly fine. However, don't give them anything too large, because they may be lying. To avoid Method 2, if the host asks for another rare in order to return the victim's rares, simply don't do it. That is always a scam.