This way, I could be flipping million dollar houses with greater profit margins and less competition from the amateurs.

Just my $.02 and my duty to protect others from taking advice during amateur hour. 

It's the mindset of a pro and an amateur. 

They may laugh at the suggestion thinking it's just full of amateur investors barking about legal matters.

Honestly from the little bit of info you’ve provided, they both sound like amateurs: Agent A for doing a bunch of free work for you and not locking down an exclusive buyer’s agreement with you, and Broker B for being a slime ball and courting you when he/she knows you’re already working with another agent.

Of course, the best place to position any business is just out ahead of one or more major consumer trends, before it becomes obvious to the amateur competition, who then jump in, bid up prices and kill the profit margins.

It can be used to identify non-compliant amateur landlords who decide to exit the rental business and sell to you.

The difference between professional and knowledgeable amateur shouldn't make much of a difference at $100k.

Like a professional, not an amateur.

Unless the landlord is an amateur then the lease language would make you both jointly and severally liable for any damages so wait it out and see if what they come up with is legit or not.