If you only do it once, I don’t see it as an issue. However, if you keep trading the item or if the person you bought it from is a known seller, then you’ll both be flagged.
if it was heavily monitored it'd be riskier than it is and noone would take risk that isn't worth the current - small profit margins on RSGP sales. As you can see - market is still running, there are more gold shops than ever.
Just don't make it sketchy and you should be just fine. RWT always comes with risk - if you commit it you have to be ready to take the consequences into the costs.
Trading items is a lot safer than trading gold imo however I've only ever traded gold and I have never been banned/warned lol. I think it's pretty safe but I would listen to what @Zuzel111 said. Just don't make it sketchy.