Flying the plane is of a lesser importance than some of the other important points presented here. An airworthy 172 will fly very much like other airworthy 172's. Yes, there may be subtle differences, and some 172's are nicer to fly than others, but it's unlikely that those fine points will be noticed during a brief qualitative flight. And, will it matter that much to you? Presumably, any snag would be rectified anyway. There's very little which could be wrong with a flyable 172, which could not be fixed. I have bought several Cessnas sight unseen, flight unflown, and never been disappointed.
If the aircraft is not airworthy, or you were to discover a non airworthiness during a sales check flight, that's a different matter. However, that's unlikely, if the airplane is regularly group flown.
When, in the past, I have flown sales check flights on an aircraft, it's been less about the aircraft, and more about the avionics, instruments, and systems - do they all work? Thus, if you intend this, be sure to have a plan to assess function and accuracy. The other aspect I have carefully observed during check flights with other pilots is how they handle and care for the plane. If your pilot is comfortable with a hard landing, riding the brakes, sliding tires, or overspeeding the airframe, that should be a concern to you. If your pilot bumps a landing, and immediately repents, don't worry too much, 172's are tough!