Have them pay for it and tell them you will reimburse them if there is a structural issue to the exterior sewer line. 

Credit score shouldn't be an issue.

This may be a case where you are trying to force the issue by wanting to complete a flip transaction where your market is telling you its not the right time.

However, if you're using a discount company that's allowing you as the owner to set the rent price, approve or deny apps, etc. then your issue could be one of many things. 

Now though, it’s a real issue because it’s affecting my rental income.

Although we didn’t have a move in move out list at the start of the lease, we have all the communication from the beginning to prove that they reported every issue and we took care of it.

Older buildings can be an issue, we had to put some spray foam around the heat pipe entries. 

I will check with my city officials on this issue as they've likely had experience with VRBO and ABB

—————-Thanks Michael,I was actually thinking about the same issue with the capital gain.

The issue with someone porting into your area from someplace else is that they almost never have income when they move.