I agree with everything you said. There are brokerage houses that have a minimum commission....so it is not always 10%(5% if co-brokered).
My boating career has spanned 22 years and 6 boats. Most of those boats have been bought and sold thru the same broker. I think the best thing to do is develop a relationship with a broker over your entire boating life. Find one you like and stick with him. You will learn each other and know how to treat each other. While I am perfectly happy with the boat I have, I am still always looking especially since I am considering the next boat to be my retirement boat. My broker just showed me a boat that I told him, straight up, I was NOT going to buy. I just wanted to look at it to see if it could be considered for a retirement boat or to strike it from the list. It took about 30 minutes of his time. But he knows when the time comes, I will sell my current boat thru him and buy the new one thru him. So giving me his time has value.
My current boat fell to half price after survey. My broker continued to remedy the situation to the point of me buying the boat. Without that, I can guarantee I would not have bought it. But he did ALL of the legwork and locating of parts and prices to get the boat up to useable/enjoyable status....all for a fairly small commission. I even asked him..."Why did you go thru so much trouble for such a small commission?". And his answer was that he knew I would be back for the next one.
Anyway, try to find a broker that you like and stick with them and nurture a relationship. A good broker will understand your intent and work for your business. And in turn, you respect his time and efforts!!!