In general, over the years, W&B have been the thing I have found most commonly wrong, or otherwise troublesome. Several aircraft I have test flown were found after the flight to have been ballasted wrong, once way aft of the aft limit - now I "reality" check every one, before I fly.
A few times, I have insited that the aircraft be reweighed - getting really foul looks for the maintenance people who have just weighed it. I can't tell you how many times they got a different result on second and subsequent weighings.
Don't under estimate the importance of having the C of G within range. The ability to recover a single engine aircraft from a spin at gross weight is often the basis for establishing the rear C of G limit. Been there, done that! Those circumstances are the very worst time and way to find out the C of G was wrong!