Bumped doesn't really matter on classifieds. The reason it matters on outpost is because bumping gives your trades visibility by moving them to the top of the list. On classifieds, the list is based on price alone. It can be an indication of activity - if someone's listing is 5 days unbumped and when you go look at their profile they've been offline that whole time, then sure, that's probably not valid. But if they're online and seem active then whether or not they bumped recently is fairly irrelevant.