Not trying to be anything but helpful here, so I apologize in advance if I come across in a way that is too direct.
If you are buying 300 pins from one seller in one auction from ebay, they are fake, period. No legitimate pin trader, buyer could possibly sell huge lots like that for so cheap. I'm guessing that you paid around a buck or two for these pins, probably less.
I am SO happy that you got the information you needed from these boards, and have sent back the pins. THANK YOU SO MUCH for doing the right thing!! Kudos to you for making the decision and using the information here to do what many don't.
I just wish there were some way to STOP these people from selling these..what is going on that is taking so long? It is SO frustrating!
In general, anyone reading this thread, who has an ebay seller in their sights who is selling HUGE lots of pins for around a buck...THEY ARE FAKE!!! That is as simply as I can put it. You don't need to research, you don't need to look on the red or green lists of sellers, THEY ARE FAKE period! There is absolutely NO OTHER explanation, NONE whatsoever at all. PLEASE use common sense when purchasing pins.
If you are wanting to trade pins in Disney, and are thinking of trading 50 per person each, you should be thinking of the actual cost to do so, which is between $400-800 dollars per person. That is the cost of Disney pins when buying them from Disney. If you really want to buy legit pins, you can find people (myself included) who sell occasionally for $2-$3 per person, which is still over $100 each.
This hobby is NOT cheap, nor was it intended to be (it is Disney after all people). Buy REAL pins from the pin traders locations in the parks and do what was intended, trade AUTHENTIC pins for AUTHENTIC pins. When the practice comes back to this place (if it ever does) you won't need hundreds to trade each trip, just a few here and there is great.
There are plenty of other things to do in Disney that are great fun and cost MUCH less!! Penny press collections are a BLAST and accessible.
I feel like I'm standing on a soap box preaching and I truly don't mean to. I just HOPE anyone who reads this, who is contemplating buying huge lots for SUPER CHEAP just DON'T DO IT. Please, use common sense, if it seems to good to be true, IT IS.