The number one thing is, if you dont know the P/O and havent seen the boat, dont assume you are going to pick it up. You are there to look, and then consider it!
Broken motor mounts, compression, test riding- which will spot out possible cooling system clogs from sitting, and fuel problems, and will certainly determine whether or not everything is working.
When you get there, feel the cylinders, if they are warm, thats a sign the ski may have trouble starting, and he wanted to get it running so it started easy when you get there. Look for any patches on the hull or stress cracks. Check the impeller condition and look under the boat at that, and also check the pump vane condition.