Is it possible to reply to a topic without bumping it? I think this would be a very useful way to warn others of scammers, trolls and suspicious posts without bumping the thread to the top where more people can see.
Hmm at the moment it's not possible although there are some sections in which threads are not bumped by the latest posts, but most section works according to the latest posts. If you have seen old posts so many times, which are bumped by some scammer, or anyone which you think was irrelevant and wanted to see the latest reply. Then use the Ninja's TG notification bot. As you can track the whole board there and whenever new topics are created you can see them and can make posts accordingly.
This way you can keep a good record of the topics people are making, I never saw any old thread on the top as I mostly visit BTC, Help, Meta, Trading, etc. sections so these are always flooded with new topics. I suggest you to use the tg method to avoid such behavior. Plus if you think this post made by X member is only meant to bump this thread and useless then report it, Although I don't think its against the rule unless it's relevant to the thread.