I hate selling cars too, tho I have been fairly lucky actually getting rid of my old ones but all the stupid "will you take 50p and a conker - I can come round to pick it up in half an hour" messages drive me nuts.
A mate of mine was selling his 10year old Volvo recently and two guys turned up - one distracts him while the other splashes some oil about under the bonnet and they then try to convince him its knackered and they will take ti away for £200.