In the case of the real estate example, I bought my last house with a broker in 2005 that saw our finances and decided we needed a bigger house x2. We hesitated, but we were eventually convinced by our broker... [I] was too polite. I felt this way with every broker I talked to.
I hope you don't take offense at this, but you need to learn how to handle a business negotiation. Your broker is not your friend. You need to learn the difference between being "polite" and being a patsy, between being "rude" and being firm in a negotiation.
Whether we're talking about boats or houses, you tell the broker what you are looking for and what your price range is. If he/she does not show you boats/houses in your price range then you walk away and find a different broker. If they ask why, tell them. If they try to apologize and plead with you for another chance you say, "Nope, I've moved on, time for you to do the same." Period. End of discussion.
There are lots of good brokers out there and it is worth the time to find one. Wasting time with a bad broker because you don't want to hurt his feelings is just DUMB! This is NOT being rude. This is simply insisting that you get what you pay for. Nothing the least bit impolite in that.
Now, having said that I will point out that, just like with houses, boats usually sell for less than their asking price. So if you say your limit is $50,000 the broker may want to show you boats with an asking price of $60-, $70-, or even $80,000. This is because, with some aggressive negotiation, these boats may end up going for $50,000. If he is trying to convince you that you can spend more than $50,000 though, walk away.
Also, there is absolutely no need to share any of your finances with the broker before the time comes to negotiate a purchase contract. It helps to tell him if you will be paying cash, or financing, because then he will know if a purchase offer will require a financing contingency. But even then, you don't need to tell him what sort of loan you have been approved for. Only that you have a pre-approval and that you want to spend about $X as your total price.
I grew up in the Midwest and was taught to be polite. I understand that sometimes it goes against your grain to negotiate aggressively and to keep saying to yourself, "it's not personal, it's just business." You need to do that, though, unless you are willing to spend more than you should to get less than you deserve. Remain friendly, remain polite, but remember that it is not rude to say "no" and it is not rude to say "you are not serving my needs, I am taking my business elsewhere."