What machine are you buying? What engine is on it? Pictures rarely show current state of the aircraft so check it out in person. Check all the logs and maintenance records. If it has a rotax 912 or so engine you could have a Rotax A&P check it out. There are condition inspection check lists that you could use as reference and go through the machine to the same level of detail. Is it a dual place gyro to take a test flight? If not you can have the current owner take it around the pattern to show its flight worthy, but that’s limited value in my opinion. Depending on the model there are specific items you can check on for common areas that can be damaged, I.e rotor damage, bent mast, cracks in welds, damaged motor mounts, scraps under horizontal stablizer, bent landing gear, etc. one common issue I found was improper wiring so can check for that and noise in radio system. Use of wire from Radio Shack instead of aviation grade wire.