Based on personal experience, anyone selling more than just single pins seems to be dubious. They constantly describe them as 'tradeable' rather than authentic - and claim they got them in the parks, only to later say they had a 'supplier', as I found when complaining to a seller. I had just got into pin collecting and wanted some fun surprise pins, was a real waste of money. I kept them rather than sending them back though, in case they resold them on, and just gave them ratty feedback. The bad sellers don't always have bad feedback - they can get rid of most ratty feedback under the pretense that it could be resolved and offer a refund, only to resell the same dodgy goods to someone else. Also their email went from being well written to dodgy, broken english.
I'd just avoid ebay entirely unless you are buying one specific pin, imo. A trader or seller really doesnt need ebay to reach their audiences.