In spite of being a frequent buyer of craigslist junk cars vintage automobiles, I hate negotiating.
Here's my technique. I call the seller to say I'm interested in looking at the car, but the asking price is a bit out of my budget. If they don't immediately say "This car is awesome and the price is non-negotiable", then I go look at it. Real-life example: looked at a VW rabbit. Seller was asking $2000. They apparently had seen that perfect examples were selling on ebay for $5000, so they thought the $2000 ask was fair. I observed that it was hard to start (bad glowplugs) hard to shift (needed shift linkage rebuilt) had mice living in it, water on the floor, exhaust was loud, charge light was on (needed an alternator), tires were ancient.. I knew that it was an $800 car. Rather than tell the seller what a POS the vehicle was, making him feel defensive & angry, I just said it was a little rougher than the pics appeared. Then i lied a little, saying "I have $800 to spend on my next project, And the car is worth a little more than that, but that's my budget, that's all I can spend." That's the cue to pull the 8 $100 bills out of my pocket that I cleverly arranged there a moment earlier. If the seller says Okey-doke, then we're done. In this case the seller said no, he thought it was at least $1200 of car. I thanked him and hopped in my friend's car to go. As we were turning around behind the barn, I could see his wife explainin how he had just screwed up by not taking the cash and getting the POS project car outta the backyard. As we drove back through the yard to leave, seller flagged us down and said "OK, $800 and you get it outta here right now." Done deal.
Postscript: I spent another $1200 fixing it up, drove it for a few years and sold for $2500 on ebay. Not profitable, but zero depreciation.