Wire transfers are very common in Europe. Checks are quite rare in most countries. In the US, international wire transfers--sending and receiving--can incur high fees, so often aren't worth doing except for large transactions.
As far as the feedback thread in the classifieds goes, we can do that, but I don't think it's going to be that informative. Many sellers here don't sell many things, and those that do are well known by their consistency.
Really, the way to know how trustworthy someone is is by watching their APUG behavior. If they post regularly on a variety of legitimate topics and seem to know about and be interested in analogue photography, if they've met people face-to-face, if they've participated in print exchanges, and they have a reputation to maintain in the community, and they generally seem ok, they are probably ok. I'd trust that more than any rating system or even feedback about sales.
If you have a legitimate problem with a transaction, APUG can't be legally responsible, since these are transactions between individuals, but contact the moderators, and we can try to help, and if we find a bad apple, we can ban that person, or maybe just refund their subscription, so they can't sell in the classifieds anymore. Most problem transactions are the result of incompetence or ineptitude more than outright dishonesty. In a number of cases we've tracked people down and helped them work things out with the other party. In the rare case that someone has an intractible problem with a seller or buyer, it becomes public without having a dedicated feedback system.