Our broker is making it sound fairly black and white - that if they show proof of funds/financing, the Seller has no choice but to accept the first offer and move forward with them. 

I told him that wasn't fair and not what we agreed to.

It's not "aggressive" or "confrontational," it's being fair, but firm. 

I think it would be fairly easy to rent out the master bedroom if I were to move out and I would cash flow on the property.

Even though it is fairly simple & straightforward, it is NOT easy. 

If they are VERY professional, they will have their processes in writing as verification that it is enforced equally and fairly by their entire staff.6.

then I would be able to let people know based on their situation if they were a good fit for coming to look at the property.It worked fairly well at weeding out the tire kickers and left me with a decent number of people to follow up with before the open house.  

Is it fair that I will only get enough to cover for my time, gas and marketing?

It was fairly quick and painless.

Purely a buy and hold at a fairly low price.