You can pay a flat fee listing service a few hundred bucks to upload a listing (you'll have to answer calls, schedule showings, set up a lockbox, get a sign, vet potential buyers, avoid scammers and people trying to sell you stuff, negotiate and manage the sale yourself).

Do you have a disclosure or buyer agreement signed with this buyer?

A certified letter is good because they sign for it, acknowledging receipt, any other forms of written communication you can get to document that they were notified of the hazard probably also helps. 

Its a tough subject because logically, they are joint and several guarantys so rationally a 100% guaranty from each of two people (one 740 one 680 for example) is ALWAYS going to be better than just one 100% guaranty from someone at 740 (so it wouldn't make sense to have a better rate for the latter)The problem is that there is fraud and "straw borrowers" out there where someone who is not involved in the property signs on to boost score and terms - so many DSCR Lenders in response either do the "non-rational" thing and price to the lower to avoid the fraud or use the higher of the two (and either be a little loose with things or just stay vigilant on any funny business)

For example, the signs of the 2008 housing crash were all over for everyone to see but many investors were blindsided by their "following the herd until the last minute before the party ends" kind of strategy and lost everything as a result.

@Maya S.In representing both lenders and borrowers, I’ve seen some solutions other than tenant signing an extension prior to closing.

Did they sign a lease or are they still considered STR?

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

Cover the boat and/or put a "NOT FOR SALE" sign on it and go about your day. 

Which would be signed AFTER the marriage takes place.