For example using AirBnB services?

That's why buyer hire inspection services to complete their due diligence before closing.

Is your loan modification done through your mortgage servicing company or handled by the BK attorney?

The assignment assigns the Mortgage to youThe allonge transfers the note to youAs for due diligence :Are the notes Dodd Frank CompliantHow much are you investing relative to the current unpaid balance (UPB0How much are you investing relative to the current Value of the propertyAre there unpaid taxes on the propertyAre there any unpaid liens on the propertyAre the borrowers currentHave the loans been professionally serviced so you know the pay history and the correct UPBDo the borrowers pay on timehow long have the buyers been in the property, do they pay on timeAre taxes and insurance escrowedIs there insurance naming the lender is there a lenders title policy

Your willingness to bring something to the table by being of service. 

Are there online legal sites/apps that you can pay for this type of service?

A local real estate attorney can draft you a note and a security instrument (deed of trust, etc) for this lending arrangement.It would be good to have a loan servicing company handle calculating/collecting payment for a small fee (like how property management companies manage your rentals for a small fee).

I am specifically looking for companies with a proven track record of transparency and competitiveness in their fee structures and excellent customer service.

They will get a 1099 for the deficiency; in the case of a deed in lieu it's generally the servicers FMV - payoff.

From this you need to take your debt service (1500 - 1700/mth) and set-aside a reserve for Emergencies/CAPEx ($300 - $600/mth).