Problem is, it's easy to sell on ebay than anywhere else. I posted 3 S5's and sold them all the same day on ebay. I could put them out in the forums here and not get any real interest for weeks since nobody wants them anymore.
This. And you can get high prices on ebay that nobody on this forum would ever pay. I sold some miners recently and I was a little nervous when a person with only 16 ratings bid on it but they sold to people with more than 30 ratings.
Are you allowed to put in the listing that you will not sell to anyone with less than 10 ratings (or whatever cutoff)? In the buyer requirements you can only select to block users who "Have a feedback score of -1 or lower" which basically means they already misbehaved in at least one transaction.
Also it seems to me that if they gave positive feedback they should be essentially giving up any right to bitch about the sale later.
Yes, you can put whatever stipulations in the auction or buy-it-now. I know eBay says otherwise. However, you do risk a negative feedback. The worse they can say in the negative feedback is you did not ship the item to them. You can also respond to their feedback stating WHY you did not ship to them and that you sent their money back to them. You can also block that buyer from participating in future auctions of yours.
I also intend to search PayPal user agreement for sellers to see how they get away with chargeback claims being charged back to the seller after the buyer has kept merchandise and made no effort to return it. I will then post that part of the user agreement in the auction or buy-it-now for the item up for sell so there is no confusion.