I'd check no play in the linear bearings and they slide smoothly, check the fence slides and tightens ok, maybe check with a square that it's 90 to the faceplate (where the cutter comes out of) when on 90 setting (in case dropped). Check the stops on the faceplate, check the depth stop slides ok, width selectors works. Don't expect it to purr (usual festool metal gearing thing).
That's all just going off first principles thinking about what might go wrong on one rather than known faults. Have a read up about how to plunge them before testing. Loads of people whack the cutter in too fast like you could get away with on a biscuit jointer, but that causes a twist in the mortice which then gets blamed on tool inaccuracy.
If well used the plug it connectors at the tool end can break so make sure it's fully engaged and wiggle it around while its on.