Check engine oil and engine air filter to see how those look. Check engine for blowby. Check main drive belt for excessive wear. Check poly belt for excessive wear. Make sure poly belt case is free of sawdust/chips/grease. Wiggle cutter wheel to check for bearing play. Ad says it has new bearings, so it should be tight. Make sure pins and bushings are tight in pivot area and pivot cylinders. These areas do have some slack, even when new, but you do not want to see a lot of slop there. Test all controls for proper operation. How does machine look? An overall clean machine with nice original paint can mean seller takes pride in maintaining his equipment. Brand new paint can mean seller is trying to hide something.
Jeff