Are you saying that you would purposely sell someone signature links on an account that has been hacked, stolen or abandoned?
No, I would do that with accounts which have been legitimately sold.
Do you disclose this to your clients up front?
Yes, I would disclose publicly which accounts I bought, and ask to the sponsor if that's ok with them.
Anything else?
How do you know that they are legitimately sold? Do you purchase them offline by a known physical person?
Please publicly disclose all of the accounts that you have bought and or sold so that the rest of us know to ignore them and not trust them.