Although Buying/selling bitcointalk accounts was widespread before Merit system, I do not remember that there were cases that successfully sold merit too
many Merits and therefore the black market for them is small and not enough to make changes.
In general, I do not know the benefit of it, as ranking-up to fullmember, hero and above required too many merit, which are impossible to collect by buying them, and the risk is great + joining campaigns does not only require merits.
It may be understandable to anyone who wants bounty campaigns and others that require a member's rank or 10 merits.
Everything is also simple here, if 10 merits are bought for the "member" rank, then, of course, you will not see more merit purchases, since for this there are sales of ready-made accounts.
Look at some accounts today that participate in token-paid subscription companies, there are a lot of awakened, that is, sold accounts. Since we already know their rules, you cannot change passwords after purchase.

There is a rule that is not to change the password after buying an account. I'm complying so this account isn't locked.