First, welcome to the forum. It does make sense to buy a new gun or a used one from a shop you know. On the other hand, checking out a used revolver yourself isn't rocket science.
Other than things you already know, like first make sure a gun is unloaded, check the bore, obvious signs of buggering and stuff like that, I only do one thing with a revolver. First, close the gun with it as close to battery as possible, ie. where a cylinder will line up with the barrel when you close it. This saves adding to the turn line. Lock up the gun by cocking it and then carefully ease the hammer down while holding the trigger back. Next, try to wiggle the cylinder and there should be minimal play. Turn the gun sideways(watching the muzzle of course) and look at the gap between the cylinder and forcing cone. If you could get a credit card in there return the gun to the seller and move on. Technical types will make careful measurements here but I don't have the interest or ability to deal with those teeny numbers. Shine a light between the back of the cylinder and frame and then look down the barrel(it was unloaded right?
). The cylinder and forcing cone should appear to line up. I only check the alignment on one cylinder but I guess you really should do all six.
The above, using the term loosely, "checks" the lock up, cylinder gap and timing. Others also cock the hammer and try to get it to drop, called push off, and dry fire the gun too. I do not unless the owner volunteers for me to as these two things iritate many sellers. I normally hand the gun back by holding the top strap with cylinder open and grip towards the seller.
A gunsmith would look at a lot more, I'm sure, but this works for me.
Bob