RakerBill

In my past experience with mower engines, especially used, or older ones, they can sometimes build up carbon on the pistons inside of the motor. When it was running, did the engine make any unusual noises like a knock, or rattle? Does it smoke at all? Either of these can be a telltale sign of buildup.
You should take the starter to a reputable small engine mechanic, and have it looked at to see if the starter is hanging up. They are not designed to take much abuse like extended cranking, as they will get hot fast. And also check both the battery cables on both ends to see if there is any corrosion, or if they are loose, as if there is, it will cause hard cranking, and the wires to heat up as well.