As someone who manages a small business, that was a poor response by that bike shop employee. If a customer comes in wanting to buy something you're selling, sell it to them whether you think they need it or not. It's different if they ask you something, say like, if they ask if they need new brakes and their brakes are fine, for instance. But someone wanting to spend money to swap a part because he likes the looks of the other one better? Sure thing, how much you want to spend?

This is why so many brick-and-mortar stores go out of business.