That being said, it's tough to get over the relatively high rate of return for STRs when you are comparing them to LTR. 

I can understand their concern, but I know people have done this.

Here is an article that goes over the basics.

I don't mind not having cash flow as I do have other lines of income however, I definitely don't want to go in negative and I do want my property to appraise over the period of time well and not give me too much maintenance headache.

And of course there is the usury issue to deal with when you go over 10%.Unless you're doing volume, why not just download a note & dot from Fannie/Freddie, it's a .doc file so you can make changes.  

You can order a property inspection report which will show you any concerns or issues with the property.

Since rarely are properties on the Oregon Coast (or anywhere for that matter) in flawless condition, generally post receipt of the inspection report there are items of concern that buyer(s) will want repaired or compensation towards. 

You always have the option of walking away.My recommended course of action is that you extend the contract so that you get YOUR OWN hvac guy can get out to take a look.Your hvac guy won't mind the quick and easy job of diagnosis, give him an hour or two of work, have him write up a lightly padded repair estimate and hand that over to the seller and ask for that amount to be credited.

I am concerned the check could be fake or the homeowner never gets paid.

Most good leases have language at the end and a space to sign over the lease to a new owner.