*You're his buddy, and you'd love this one favor...
*You simply can't afford anything more
*Look up the price on KBB or NADA, and tell him it's simply not worth that much, and you can get one for cheaper at the local dealership.
*Old bikes, like old cars, break down more often, so it would cost you extra money to maintain it.
*be super nice, courteous, respectful, and kiss lots of ass.