Define 'within Jagex rules'. It could be considered under 'encouraging rulebreaking', making it more likely that the host will item scam (which would be an offence by the person giving the money, not recieving). I think the reason it's frowned upon is the same reason we do not allow advertisements of dicing on Tip.It, that is, it's far too likely to be a scam. Courtesy of the high level forums: