Don't blame the forum. Blame the people buying old accounts and paying spammers to participate in signature campaigns. They're the ones funding this nonsense.
Why shouldn't I blame the forum? The forum rules have flaws and I am a member here. If I have an issue, I can't speak about it? The forum is letting people to create more than one account and hence inviting spammers to spam and scammers to scam. When the latter happens, the only thing is said "Scams aren't moderated."
If the rule of creating more than one account and selling accounts is stopped, then that will be a positive change else everyone should just bear the flaws as of now.
I think OgNasty expressed a valid point, also if the forum staff will put a rule don't you think a lot of users will 'bypass' it? This is the unique reason why buying & selling (or have more than one) forum account is not forbidden... because it is impossible to stop this practice.