Depends on the person mostly.
Make sure that when you do buy an account though that the account is theirs and they are the original owner. Otherwise, when you find out that he wasn't the original account holder, things get SO complicated.
Whoever you buy the account from needs to have a good reputation and can be sure that they will help you out if you do lose the account somehow.
I had 3 instances of an account recovered back from me. Two was rare name accounts and one was a one letter account that had around 10 owners so yeah that's what I am saying about the original owner part. Huge risk of losing the account and getting it locked.
The thing was though that these 3 accounts were from trusted and reputable members with 100+ vouches so in reality, it will always be a risk at least from your side of who you do trade with.
I have around 50 accounts though that I am not the original owner of that I have kept at least 6 months+ without being recovered so definitely you will have a greater chance of getting a good account than a bad one.
Just look around, check their vouches and reputation. Remember to ask for some information as well in case you will need to recover it or lose access to the account. I would say the best info needed is previous passwords, account creation date, location account was created from and the service provider used. Still ALL accounts can be recovered regardless.