When i click on a comic book it might say 5users have this, but I can't figure out who those users are to make them a offer. There's only one person I can click on and that's the person that edited it last.
As users have the option to keep their collection private, there is no way to now the owners.
I'm not sure but I think that they have disabled the ability to buy & sell. Check other forum questions but I don't think that they were able to do the site the way they did discogs.