A scammer says that they're doing a safe wheel giveaway. 'Wheel' is a fair way of choosing a players to give items to. A giveaway host goes to a digital wheel-spinning site and types everyone's names on the digital wheel. Whoever the digital spinner lands on receives a prize.
Sometimes, a scammer will require rare items from players in order for them to be put on the wheel. Since the prizes during Giveaway Wheel Scams are usually large, you might be willing to risk rare items to get a chance at winning.
Alternatively, they may put everyone on the wheel without asking for rares, but then offer more spaces/chances on the wheel in exchange for rare items. For example, a scammer may say that the prize for their wheel giveaway is a Black Long, and that you'll get one more space on the wheel for every Den Beta you trade them.
How to avoid this scam
If someone asks for rare items to get spaces on the wheel, don't give them items. This kind of wheel 'giveaway' is always a scam. If it looks like someone won the wheel, it's a spare account or helper. If a scammer isn't using a spare or helper, they lock the den without giving anyone a prize.