All of the postcards I have on eBay right now are from my own collection. They were either sent to me through the post, via mailing lists, at the time, or collected from gigs and other places.
The condition of most is as-received in the mail at the time; they have my name and old address on, perhaps a bit of a light scuff in the corner, they've been through the mail. The odd one might have a fold or a drawing pin hole in. Generally they are excellent, the poor condition ones I didn't keep.
I have a large number of mid-1990s indie / Britpop postcards on eBay right now, please see my other auctions for more.