UDID purchasing is one of the safest and scam free purchases out there.
Here are the pros and cons for what happens if someone on either party attempts to scam another:
Pros for Developer:
-None
Cons for Developer:
-If Developer deletes an UDID slot, they will not have a new available slot left. If they have 32 remaining slots and delete a past one, they will still have 32 slots left.
Pros for Purchaser:
-None
Cons for Purchaser:
-If Purchaser attempts to claim back his money, the developer can delete their UDID at any time which will result in a useless iDevice if they were running iOS 5.
