Home was purchased with cash and all rehab is being done by ourselves and paid for in cash.

When one stops the other is on the hook for the entire rent.What exactly are the tenants planning to do, is one leaving, is one staying,  have you been paid all of Augusts rent, if not what have you done about it.If they owe you rent do not serve them with a N4 as that will allow them to be absolved of owing any rent.What you need to do is asap file a L9 to collect money owed.

Had one guest stay for 2 weeks and they apparently paid with a fraudulent/stolen credit card, VRBO approved the payment and stay.

Can anyone provide me advice on how to approach pre-foreclosure properties?

I didn't use them at all but I paid for the middle package where I could email them questions.

You should have your own pre-screening system before you charge them.

I have been on the hunt for finding REO or pre-foreclosure properties.  

The property is paid off and I'm thinking about getting an Equity Line of Credit against it to buy a 250-300k house in Atlanta to flip and rent it.

Since I ended up putting so little down on my primary and have savings left over, last week I was pre-approved for 25% down on a duplex out of state at 4.75%. 

However, I have a comfortable allocation of secured funds for investing and there other reasons I believe I'd qualify for other loan options.My question is, how do I see about getting additional pre-qualifications on identified properties/home values without lenders pulling my credit?