Lots of good advice, but I think it's critical for anyone selling anything to remember that it's much harder to sell an item than an idea. If people actually made buying decisions on things like if a car runs, every car salesman in the World would be thrilled to death as they would be able to move cars all day long.

The best salesmen don't sell cars, they sell ideas. They sell the idea of you driving their car in way that stirs your emotions. You achieving your goals sells something more than the object itself.
Perfect case in point. I had the 360/904 yanked from my 74 Road Runner so a 440/727 can go in, and I needed to offset the costs of the 440/727 by selling the 360/904. After doing some checking, I found the average price for a complete and running 360 is about $550, and the value of a 904 tranny is about .28 cents. Problem was I needed about $1,300 to be where I wanted to be on the 440/727 costs, so I listed the 360/904 for $1,500. I made sure the ad had pics of the engine and tranny, but I also added a pic of my car with the hood down. Why? Because I wanted the buyer to see the 360 callouts on the hood and think how cool it will be to see
360 on their car. I then mentioned how 360s are pretty scarce (as compared to 318s), which sets the idea the engine is hard to find. Then I mentioned how paying $1,500 for my 360 was a lot better option for upgrading from a /6 or 318 than spending $3,000+ for a 340, which sets the idea they are getting a bargain. Lastly, I mentioned how this engine would be awesome to put in an A body car because of the performance it gave my B body.
I ran the ad and had four people contact me about buying the engine. I made a deal for $1,500 from a guy at the speed shop I ended up going to, but then the deal fell apart early last week because he couldn't sell the engine in his 66 Valiant. So I relisted the ad on Craigslist last week on Tuesday, and immediately got called up by a guy who had a 318 in a 69 Barracuda and after reading my ad decided now would be a great time to upgrade to a 360... wonder who put that crazy idea in his head.

I sold the engine again, and when I took the money to the speed shop, the owner told me how he couldn't believe how I had sold that engine that fast since there isn't a lot of activity in that market after tax season, and I told him good ideas are always selling.
So I was able to sell an engine for close to three times what the market price is, twice, by focusing on selling the idea of buying a 360 and putting it into a car rather than just trying to sell the engine itself. This stuff does work if you do it right.