In the music community people on Instagram making generic comments like "This is fire" is seen as a problem to a lot of content creators because they want real feedback. Not a bullshit comment that is only design for you to check them out. Internet gurus such as Gary Vaynerchuk promote the idea of commenting and direct messaging puddle on Instagram you want to work with. Others echo the same idea because the belief is that social media sites reward user who are active on the platform. Plus people will checkout your profile if you say something positive about that person's post. Now that you know why people do it. What do you do about fake comments on your instagram? Engage with that person. Ask them what they like about it. Direct message them and ask questions. When a person comments on your post. They gave you the green like to  with them without you looking like a spammer. Besides you never know that person may have knowledge or a connection you currently do not have. This is a great way to expand your network. There's a few people I ended up doing business with just because of a comment he made on my post I knew was desire for me to check them out. Also when you take the time to have a real conversation you will get useful feedback. So next time you get the annoying generic comment on your post. Make it work for you.