I can't agree on the "always" part of this rule.
For the two XR650L's that I've purchased (so far), I was happy to pay the asking price and felt that I would be cheating the seller to offer less than that. On the second one the seller dropped the price an extra hundred from what he had been asking before I started taking about price. I wasn't going to talk him back up, though.
When I find a bike for sale at less than what everyone else is asking and it's in decent shape and I think it's worth the asking price, I'm happy to pay that without further negotiation.
By the way, anybody know of a good deal on a used XR650L? All 18 of the ones currently for sale locally are priced too high.
(There's one apparently insane guy in Hercules who wants top dollar for everything he's done to the bike including full out the door purchase price.
)