Some just come on here to sell their unwanted items they no longer want, selling for way less than they paid that’s fine.
Others we sometimes spot that they are selling sponsor supplied items, they are a shop or there’s those who buy items and sell them on at a profit. Finding evidence to this can be tricky at times. Then of course we have those that make items, not for a living mind, for a hobby and sell on.
IMO it’s also about contribution (irrespective of whether you feel posting anywhere other than the classifieds is a ‘contribution’). A quick glance at someone’s history gives some idea. Which is why I don’t have an issue with some users selling their own kit, whether they pay traders rates or otherwise, where development and testing is often part and parcel of the forum more generally
But the whole classifieds thing is not just a problem here, especially where it’s a platform to avoid eBay fees etc and presents an opportunity to scam someone. Most forums will have their share of the former and latter, as well as lurkers who are either there to solely get a bargain, or pick up something to sell on elsewhere. Some other places are more self-regulating where there is often preference given to regulars. The problem then being everyone gets accused of being cliquey…