The risk to my business is much too high just so the agent can make a little more money on the transaction. 

Definitely open an LLC if you haven’t done so already and once you have a couple under your belt, you will have lenders lining up for your business.

Don't apologize, don't explain how the 'chosen' tenant was more qualified than they were, wish them well in their search.You're running a business and you've made a business decision. 

I dont know your business model exactly but I assume you collect some referral fee from the supplier?

Having the seller carry a second is not a problem for the first, as long as their business with you is finished and the loan has closed.

I live in Phoenix and my business partner and I put on a couple local forums for investors like yourself to network.

STR's don't create real estate value they are a business  I have a dozen and am building 2 more this year so I like the business model and I have over 100 regular rentals.   

A personal liability policy "MAY" extend to one or two rentals but if you are planning on building a portfolio consider the commercial umbrella.Another thing to consider is that the courts frown on carry high personal liability but low business liability when trying to hide behind the vail.

It's a business - acquiring/building, managing, and growing a business. 

I think you just have to work it in as the cost of doing business.