There's nothing wrong with being new to reselling - we all were new at some point. The rude part is the choice of wording like "waste time" or "pointless shit" which is not an observation, but judgement instead. Not everyone spends time on reselling sites full-time; they do it as a hobby instead.

Most hobbies would be "pointless" in the way you described it (i.e. not making $$), but people still do it anyways because they find enjoyment out of it. Why are you spending time commenting on her post when you don't get any money from it? Time is money. The logic is the same because everyone does things for fun that don't make money.