Charles, the mprep comment was at a time the forum didn't have much traffic and it was necessary to entice people to the forum. Now, account sales and multiple accounts are big offences, especially if one enrols more than one accounts in the same campaign. Sometimes, I think people have got tagged for having alt accounts even when they didn't enroll them in the same campaign or bounty. So, I am thinking having alts is outlawed here. Well, may be not for some selected individuals.
If the purchased account is found, there will be no blocking, but there will be a warning in the form of a red label. And at the same time, the meaning of the purchased account is simply lost. But yes, the forum does not prohibit buying.
But your second comment about alternate accounts being flagged even if there are no violations is incorrect. You can have many accounts if you use them without breaking the rules. There are no privileges for anyone, sometimes people need a couple of accounts to use them on different devices. But if we talk about the numerous accounts, then you can guess for what purpose they were created.