If the rack is worn, there'd be excessive right and left motion of the steering wheel with no movement of the wheels. You could compare the amount of movement of the steering wheel while the wheels are straight and also at the right and left locks for a clue as to the extent of wear. If the play is similar at all three locations, the problem may well go to another component - tie rod ends, (or as @dutchzcarguymentioned) differential air pressure, different tire tread patterns, any of the three alignment variables, etc.
You mentioned you had a concern with a shop's possible non-understanding of how to properly align the car. How do you know the last shop had a clue?