"Is this something that bothers you?"
Yes, very much, but at the same time no. It really depends (see bellow...)
" Does it make a difference to you if you are selling or giving stuff to someone, whether they are a user, a collector or a reseller?"
This is where things must be clarified, I mean, nothings wrong with someone wanting to sell something that they got legitimately. If someone asks for something for personall use like: " allways wanted one of these" etc... it's an outright con to go out and sell it right away for 10 times the price as some people do. That's the only one situation that really pisses me off and it doesn't matter if it's reality like with other 2nd hand markets or not, it's just downright wrong. A good comparison is if you get a house for a nice price from a friend cause you can't afford it at normal market prices or just ask the favor from him, and then sell it for 5 times the price! Wouldn't you be pissed with that guy ?
"How do you go about buying amiga stuff?"
Honestly ? I search both eBay and Amibay for past auctions / listings to see how much they go for. Then, if I don't need the item (very common with Amiga things) I wait a few months, checking now and then, till I manage a good deal. If after a few months I don't get it I either give up or buy it for the "normal" price.
By the way, my understanding is there have been very good bargains on Amibay now and then but, from my limited experience there, the site's policies make it look like it's supposed to be kind of a favor among Amigans that prefer to sell it to another user rather than a speculator. I think that's fair and it's great there is such a site, it's also your choice to use it or not. You can also try to sell there for a very high price if you want to and many do try, no problem at all..
