Hi Zippo, right now is getting towards the better time to buy. Right before the season, and during you'll see the highest prices. Now that the season is ending, the demand isn't as high.
I'll give a start to things to look for, but i'm sure others can contribute more as well.
The most important thing I would check is compression, and read the spark plugs. This will tell you a lot about the condition of the engine. Also, just keep an eye for corrosion, rust, and other items that you know shouldn't be there.