I decided to put my minivan up for sale. I had a reply within minutes. The guy showed up with three of his friends (this should have put me on my guard).
While I was finishing clearing snow from behind the van, I noticed the hood was up. Didn't think much of it, I mean I always look under the hood. Rode with guy on a short test ride. Afterwards, he kept trying to get me to give a price but I told him to make an offer.
Then, one of the friends kept trying to point out oil leaks. Ok, there's some power steering fluid seeping around the pump; it's a fifteen year old car with a quarter million miles. Then finally, he opened the overflow tank and showed me the brown milkshake inside.
I had seen this scam before on YouTube. One of the guys had put oil in the coolant overflow tank when I was occupied clearing snow behind the car. Then, they were going to try to low-ball me because it "needed a new head gasket". I immediately and firmly told them to leave, and they did.
I'm going to be a lot more careful in the future!
I drained the radiator (all the coolant drained out clean) and removed the overflow (which is a hassle on this van) and cleaned it out. There really wasn't much oil even in the overflow tank. I think it was just sitting on top. So it was less of a disaster than I was expecting.