I think my all-time record for this was a couple
of years ago when somebody mailed me out of the
blue to offer 1/10 of what I paid for my eyes-open
Rezo dream cel.  That was a real head-scratcher,
let me tell you.  But as the previous posters
said, you can't really consider it an insult
(unless, of course, they write back to say you're
an idiot for spending so much... which hasn't
happened yet :).