You may also be limited to the broker that lists the contract that meets your requirements.
I am no lawyer but I would be shocked if it were legal to not present an offer to the buyer (unless maybe the buyer tells the agent not to present them with anything less than X)
I personally would not sell something thru such a place, as it is MY property and MY right to decide on the sell price.
Anyway, just wanted to add on, that when you do make an offer, I would put an expiration on the offer. If it one where you have a few possible contracts that can meet your needs, I would put in an offer and say it is good for 48 hours only.
Some sellers seem to **** around, while the other contracts you could act on get swiped up. And when we all get notifications on our phones instantly, even 48 hours is pushing it in my eyes.
If a seller cant get back to you in that time, then move along.