In the latter case, I would still use QB to enter info provided by the 3P servicer and to maintain my general ledger for the lending business.

yes, its a people business.

They make their money off of real estate agents, but real estate agents are the worst people to make money off because they are highly unreliable and in and out of the business when the market changes.Their target should be the consumer with higher levels that they can subscribe too for data, since Zillow is linked to the MLS now which makes their data somewhere more reliable.

Make sure you do business with people you have vetted and are confident they will get the job done. 

If they are too busy or too lazy to answer a call or send a short email, what else are they too busy for?

Just my personal opinion - get a mentor or a person who already has good experience running STR business, preferably in your area (but not 100% required). 

The Exclusive Right to Represent makes sense for prospective individual homebuyers, but for real estate investors, it seems unfair and limiting.

Lee Arnold is by far one of the best people in the business.

For this reason, I teach people to set policies for renting to unrelated individuals.

It separates your personal assets from your business, providing a safeguard if any legal issues arise related to tenants or the property.