As I understand it, the motors have a vertical shaft with a helical gear that meshes with another gear around the pedal shaft.
Seems it would be relatively easy to insist on pedal assembly removal and inspection, along with inspection of the bore where the pedal shaft runs.
Unless those parts aren’t removable on professional bicycles...
The bottom bracket is removable and should be done so for inspection. The biggest giveaway, however would be the drastic change in weight. No biker of worth would have a bike that weighed more than 15-16 lbs. The lighter the better, which is why carbon fibre is so popular.