(Not as part of my consulting business, just as an opportunity for me to learn and perhaps build a relationship?)

Most of the time a newer or unsuccessful agents will host open houses as they build their book of business.

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

It's just the cost of doing business.  

Trusted by 50+ businesses across [region/industry]."

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.

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.   

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. 

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.

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