(not counting our Home Depot credit that is temporary and will be paid off in a few months).

You need long term debt to make the property cash flow. a HELOC is more like a credit card, it's a revolving debt.

The buyer made it clear she wanted to refinance it in a year once she improved some credit and could acquire an FHA, which I was fine with.

And finally, make certain you hire a good inspector - you can try to get credits from the seller (based on repairs the inspector finds) plus it's essential to know what you're getting yourself into, property and repair-wise.

How low of a credit score should I accept?

I may never see a dime but at least it sits on their credit and possibly stops them from damaging someone else in the future or keeps them from qualifying for a car loan, home loan, etc.I hope you've learned the following:1.

Pull out line of credits on them? 

Fantastic to see how well you have been able to do over there, a credit to you. 

It's not out long enough for a bank or credit union to see return. 

They also report the individual to a credit reporting agency so it sits on their credit and hopefully stops them from scamming the next person.