I wouldn't put any stock in what these online services generate, good or bad.

ive got a potential seller with an existing mortgage left over of 190k an the home arv is abt 310k how would i go about my offer price formula with the existing mortgage? 

Is your DSCR ratio greater than 1-meaning are you cash flowing (according to the lender's criteria of mortgage, property taxes and insurance (and HOA) if applicable).

Because I would not sleep at night knowing I have a mortgage on a property that someone else is responsible for paying.

The most obvious is that you will be able to offset your mortgage with renting out a few rooms.

Hopefully tagging Fayetteville here will get some other investors on your radar and you could start a small online group. 

She estimated we could loan up to 500K on a mortgage with 5% down at a 6.8% interest rate. 

Not bad here in Sac though since everything is online from turning tenant request called RFTA to rent negotiation through email, landlord portal, direct deposit set up.

The seller needs moving money, there are oftentimes an arrears that has to be paid on the loan, there are oftentimes HOA fees that are due, there are title costs, there are escrow costs, usually there is deferred maintenance, you have to make mortgage payments out of pocket until you get a renter in there, you have to pay utilities and taxes, and you need reserves in case it all doesn't go as planned.3.

Fill in those two numbers into any online mortgage calculator, and it will tell you what the maximum loan is.