Bad traders

pffft at the end of the day it is just biek.

Maybe there is a place to report it privately with links and the admin can send a gentle pre-written 'nudge' to that person in a PM that if they get a good price for something, it would be nicer for the forum if they resold it on the forum at a similarly good price - Gives somebody the benefit of the doubt before they are publicly criticised and it becomes heated.

That tackles newbs, who might be unaware of the rules and etiquette that come with the forum.

Regular users that skirt the rules tend to get a bit defensive or dismissive when you call them out.

Yeah, I know what you mean, but we can let them be defensive, it's such a small misstep and maybe they've just worked a 15h shift in a care home and didn't stop to think. Or they work for HSBC and love money....either way alot of people will get defensive if they're shamed on a public forum.
If they regularly take advantage of friendly prices to turn a profit on ebay, ban them.

I hear that.
This statement should apply to all users

Yeah, the nuances of behaviour on a forum and classifieds is always tricky to get right too, isn't it. What is a good price, what is an offensive price that deserves criticism... or innocent naivety or somebody hard-up needing every penny etc.