Yes, that's a really annoying thing. Often there are bots behind which are going on the narrow path to put a mix of irrelevant comments under well written posts. I had a case where a whole army arrived and spammed one of my post. There is a abuse channel by minnowsupport on Discord to report such cases. After flagging and downvoting them it is often obvious for users because of the low reputation. But it is a never ending stream of them.. @lukestokes had many posts about that and i help other Steemians in some cases to get rid of these scammers.