I just looked at the first page of stuff I've recently bought, and 13 out of 14 ( I didn't go back any further than that) were BIN purchases. I do a search on there often for something specific, and either know what it's worth, or what I'm willing to pay. Most of the time, I can find what I'm looking for cheaper than on Amazon. I haven't sold anything on there yet, so I don't know anything about any of the fees. I just skip right over all the ridiculously priced stuff, and don't even waste time laughing at them any more.
I have offered a lower bid sometimes, when it's an option, but only remember a couple where the seller accepted my offer. So unless it's a several hundred dollar purchase, I don't spend time haggling over it.