Not sure what you mean about pay to play, but if you mean pay to be in a coaching program, it can be fairly expensive. 

Hi, Frank, if the seller only has one year of income and expense data, how can we figure out the right number to purchase?

What if the new owner backs out of the job and gives it to their "regular guy", will the original contractor come after me for any expenses/materials spent?

These are expensive lessons and you will gain alot from it.

Revenue is not profit though...you have additional expenses in STR (close to 50% of OpEx) due to cleaning, vacancy, and supplies.

If you have paid much upfront, you can cancel the transaction and then wait until the seller gets everything ready.It also sounds odd they are charging the 2500 origination fee without the loan closing.

Most of the really good data is behind paid firewalls.

The only cost the deal needs to absorb that's relevant is the interest, and even that is really just the delta between the actual interest paid and the tax savings on that interest on your federal return. 

This causes at least a second trip charge from us, resulting in more expense for the owner for something that could be easily diagnosed and repaired with parts we stock on the service van. 

She does have good credit and has paid taxes for the last 3 years.