It's not across the board by any means, but there are most definitely areas that are suffering.
Don't really know much about stamp collecting, but I would imagine that it's one of those things that are "nice to have", rather than "need to have" and as such, suffering with sales.

Have you tried selling on other sites etc?  
I would imagine that there are specialist type sites for that kind of thing, which would be place to go to.

Maybe it's worth reviewing what you are actually selling and expanding range etc?