why are used merc values so low

hi i have a 2000 s320 lwb (159,000) fmbsh with all the toys (electric heated,cooled seats allround, sat/nav, tv, keyless go plus loads more)
now its in great condition with no rust or marks at all and everything works as it should, but when i went to get some online valuations they say between £500-£1200:(
thats seem very poor for a car that cost when new in exess of £65,000
is it just me or does that seem very low?
mark