This Bruin does not have any type meter or odometer. I took the previous owner at his word based on the condition of the machine.

 

If it has no speedo another way to tell if it has low miles is if it has stock Maxxis tires and they are still in good shape.

I'm on my second 350 Bruin/Grizzly and my friend also owns one. All three had a speedos , maybe it's only a Canadian feature? Looks like this one but ours are in Kilometres not miles.
I see what you mean some do not have speedos (bottom pic)

 

The condition of the machine is a good indication of miles and hours. 20 hours and the tires should be almost brand new, stock tires on most quads will last easily 200 hours or more. My Grizzly still has the stock tires with over 3100 miles on them and they still have decent tread left, probably 40-50%. With about 20 hours, plastic should be pristine, metal parts should have no paint chipped or rust on them. Basically the machine should look almost like it just left the showroom. The racks should be in perfect shape, not bent or chipped either. Brakes should work perfectly etc. A lot of quads don't have odometers on them. I think it is rather peculiar that he mentioned how many hours it had on it as he had no idea how to tell. Id just say that it is in like-new or mint condition. That would be a more accurate description.