Used phone - check IMEI/ESN and finance balance

I'm considering buying a used AT&T phone, but I want to check whether there are issues that would prevent it from being activated or unlocked.

I have checked the GSMA blacklist and the IMEI is clean, but I understand that AT&T may have an additional internal blacklist.

I also understand that if there is a finance balance on the phone that AT&T will allow it to be used on their network, but will not allow it to be unlocked and will not allow anyone but the (unknown to me) account owner to pay the balance.

Two questions:

1) Is there a way to check with AT&T whether they consider the IMEI clean?  I know I could purchase the phone, get an AT&T SIM and try to activate, but that is too late.  I want to contact AT&T before purchasing and see whether the IMEI is ok.

2) Is there a way to check with AT&T whether there exists any unpaid balance on the phone?  I know that they will not disclose the account owner's name or the balance amount, but I just want to know if there is any balance at all since that would be enough to know that the phone can never be unlocked.