You're fine.

1) So when people sell their Bitmain accounts like this, I am to assume that they pre-order the miners before they sell out, and simply don't complete the payment and leave that for whoever buys the account?

2) I'm assuming we can change the password, email, name, address, everything on the account to prevent the seller (you) taking back control of it somehow via social engineering?

3) How much do the accounts typically go for - and how much are you asking - since all we're paying for is the ability to purchase the miners, and not the miners themselves?

4) Which batch of miners were these from?