I won't be blocking boost advertisements, as far as I'm aware it's as legal as selling dungeon boosts. You'd be better off adding something to _CCleaner.
I realize some of these probably aren't genuine players and are somehow affiliated to sites selling them for real money, so if there's actually websites being directly mentioned/advertised I'll add those.
I think it's probably safe to assume any message advertising RGB boosting that mentions PayPal (like the last one in Znuff's post above yours) is selling the service for real money, which is not "legal" and should be reported as spam.
Even mentioning a "website" is probably suspect, and I'd personally report it if I saw it, but it's your call whether you want BadBoy to make that assumption.
Yeah, he edited in the PayPal stuff after my post :P However, it would be good if people report if they are seeing the exact same messages. I'm noticing that 2 of blaze's messages are exact same as Znuff's and as far as I'm aware they are on different servers, seems suspicious.
I think Funky meant the messages themselves were suspicious by virtue of having been sent to unrelated players on different servers, not that you were suspicious for having received the same spam messages as someone else. :p