As stated by Jesse, race car scales work best and are more accurate. I have an A&P/IA friend in North Florida who owns a set of Intercomp Racing
digital scales and they work amazing. I just used them to re-do my W&B after a few mods and help a builder friend weigh his brand new build for his POH and other records. They give you each wheel weight and a total. His kit has 4 scales and of course I only used 3. He also does W&B on helicopters so 4 scales are needed.
Also as Jesse pointed out, make sure the plane is level on the scales or it wont read the weight correctly.