When they get too comfortable they can stop working. 

I've stayed in a number of STR I would classify two types: 1) a house with full service as in linens minimum 500 thread count, the house has a view or is close to vacation amenities, full service kitchen with full table setting to create a gourmet dinner... these rent starting $200- 2000 a night depending on room count 2) a cabin in the woods where I can get away from wifi and be in nature with comfortable bedding and modest kitchen these rent from $80 -100.

@jason chaseWhat your lender is asking for is what we commonly call a "comfort letter".It is a checkbox on their list, and will be scrutinized with the attempt to shift liability to the accounting firm that wrote it should the loan go south and the lender cannot collect from the lendee.The AICPA as well as errors & omissions insurers strongly discourage tax and accounting firms from writing these letters. 

Now I'm thinking about converting it into an AirBnb instead to maximize my profits.

Keep your investment near the T lines to maximize possible tenant base. - What is the customer avatar (for a lack of better words) of a MFH tenant?

I've sold multifamily to a lot of owner occupied clients and everyone goes about a different way based on their comfort level.   

I know a lot of realtors in the area but none that are so fantastic I would feel comfortable recommending.

If you aren't comfortable estimating costs on your own or aren't willing to put in the work to learn how to estimate rehab costs then you need to team-up, partner, or hire someone you like a GC as others have mentioned to help you with this process.

This "re-training" has been addressed above as well but giving them the perceived control of depositing at an institution always seems to make them comfortable.

The best option for a buyer/seller rent back is the PITI of the new buyer, however, if the seller does not agree to that I would suggest whatever you both agree to that you are comfortable with while they stay there and also have a security deposit held in escrow including the rent.