I hate to sound impatient, but... seriously,
the guys on here that haven't logged in for 438 days and have 134 items listed need to go. Numerous times I've been on an interesting soundtrack's page and saw that there's one for sale, only to check it and be disappointed because it's just the guy that hasn't been around in over a year.
I get that we're all just your average VGM collectors here and that we're not businesses or shops and that we all have lives, but when you list something, you should check this site. Once a WEEK would be, like, incredibly easy, and also bare minimum in my opinion. Give people the courtesy of response. I think that without a doubt, if you have not checked this site in a month, that you marketplace listings should be either hidden somehow, or just pruned. The "Marketplace: 1 for sale" link on so many albums is in fact false because there isn't one for sale; that person is no longer around, and thus it is no longer for sale.
Anyway, I think it would be a good idea to do something about seriously inactive sellers, to start.