I blame it on all the reality stuff on TV these days, (and I admit, I'm hooked on some of the guff too); everyone thinks they can go in rip what you're selling to shreds, make an insultingly low offer and "bid" you down.
Trust me, it's often no better selling a high spec car or component.
I have no problem with anyone wanting to negotiate or do a bit of a deal, but you've got to know where to put your opening offer. Or I, (and many others) am just going to laugh at you and call you a dangler. Likewise, doing the heavy slag off bit, isn't going to make many sellers think "Oh dear, I seam to be mistaken, I'm actually selling a lemon rather than the pride and joy I've lavished thousands of pounds and untold hours of work on, that I thought I was selling", it's just going to put the sellers back up and make them defensive.
Still, some good has come out of it, you're keeping the car. That's great news!