I don’t think that BST posts should count, kinda like Unrelated posts. I don’t believe 200 post’s of the word “Bump” is more worth of counting than Unrelated posts. I think It would help sort out the scammers from others.
But unrelateds do count. At last mine do.
Nothing we can do about that.
When you are using posts to gauge the credibility of someone in the B/S/T, you should research the “quality” of the posts, not just the “quantity.” When you look at the member’s profile, click the link of their most recent posts, and actually read them to judge the credibility. Look for posts that are well thought out, have been proofread lacking typos, ones that are engrossed in discussion, proper grammar, posts that actually initiated new topics, posts with links to other accounts like Youtube or a picture sharing site, look at how far back they go, and so on. Think quality, not quantity. I would rather see fewer quality posts, than a ton of useless ones.
While the word “bump” may seem useless, it shows an “active” warm body behind a computer, someone interested in promoting the thread. While they could be a scammer, it differentiates between an active scammer and a lazy one. I even analyze the bumps to see who I might be dealing with. 
I’m going to agree with TotalArtist on part of this.
Trader rating can be used to gauge credibility.
Bumps show last activity of interest by a seller/trader/buyer in a thread. When I shop BST, I typically ignore anything with no activity of 10 days or more from the current date.
I also appreciate it with BST’ers trim their threads to remove excessive bumps. If you’re taking me off the first page, it gets annoying. People who want to buy or sell or trade want to get right to the stuff right away.