Primer's just an intermediate type of paint. Y'all might like magnets, but you can walk around casually tapping the side of the car with your bent index finger's middle joint and be a little more inconspicuous about it. Won't generally scratch the paint either.
The ultimate check for metal smoothness is a colored translucent clip board. I saw that in use at Mopar Nats one year. Almost like a portable neon light bar. EVERY surface change will be very visible. Not sure how it works at night, though, but works great during the day.
On the vertical surfaces, it could well be just "dents", but placements on the vertical areas of fenders and such, more issues could be there.
Enjoy the hunt!
CBODY67