For me, somebody coming with a checkbook and asking me to put a price for my bike is just bravado. If you want something, you don't show so clearly that your budget is that high.
I have the feeling that the people who has been able to make so much money to spend it on whims like a motorcycle, has not made it by showing their interest when they want something.
If people ask you to buy your bike, tell them to put their money where their mouths are. Get serious and talk about money and arrange to meet next day, and see how many of the "checkbook guys" are indeed willing to get the pen out of the pocket for the signature. Both of you can talk about business and retract at any moment before the handshake, so there is nothing wrong with it, as long as the other guy asks first. If the other guy was bragging, you beat him in his own battlefield. If the other guy was serious, you tell him you just wanted to check whether he was or not, and that you will seriously consider his offer.