There are markets that are very saturated with STR and with vry bloated prices and high interest rates it could be impossible to turn a profit at all. 

They mentioned that the rate will be higher if locked for 5-6 months.

(Quoted about 8.5% rate on a DSCR loan, and budgeting 10% of rents for capex, 9% for PM, and 5% each for vacancy and maintenance) After-rehab rents would be about 1350-1500 based on comps.

If it is being sold as-is and they are only entertaining cash offers, it could be because the house is not habitable in which case a bank won't touch it with a mortgage. 

I'd start by talking to a mortgage broker/loan officer to find out how much you're qualified for. 

I am paying mortgage for all the rentals from business accounts.

Rates will be in the 5's right now.

Their true vacancy rate was roughly 13%, not 1.5%.

Different exit time-frames, people missing payments for mortgage and taxes, who pays for repairs, what happens if someone moves, what happens if their life situation changes. 

-Buy the property for 715k (It appraised for 700k)-325k loan on the property with 390k equity-SubjectTo Finance the 325k and take over the mortgage/deed-Seller finance the 390k equity at 0% interest for 2 years and 6% interest for 13 years with a 20k down payment paid over 6 months.