I only read the first post, so I'm just going to point out this typical internet scenario which I have seen many times:
Person A: I just bought product brand X! Yay!
Person B: You should have bought product brand Y instead.
Person A: :(
In this case, Person B is being a richard. The only possible goal here is to make Person A feel bad about money they have already spent. If you find yourself in this situation as Person B, you should just ask them how they like it or some other polite small talk.
This is in stark contrast to the pre-purchase scenario:
Person A: I think I'm gonna buy product X!
Person B: You should buy product Y instead.
Person A: Really? Thanks buddy, you saved me!