Do mechanics see gps tracking devices on cars often?

?? Well all the new “conveinence” systems such as OnStar and its equivilants are by design GPS trackers. Thats why I would rip it out ASAP

Don’t forget to pitch your cell phone too.

The only vehicles I’ve seen with actual physical GPS transmitters as standard equipment so far are government owned courtesy cars for employees, Hydro trucks, Bell vans, ambulances, fire trucks and police vehicles.
That is besides your usual in-dash GPS system that doubles as a transmitter and of course things like OnStar.

they can track your cell phone, nav system, on star, and i have a few parents come into the shop and have us put a tracker in their kids car.

Answering in order: Yes it is normal. No we typically don’t inform customers unless it’s something effecting the operation of the vehicle. Yes we notice those annoying, cheap and often dangerous third party devices you’re using. And yes often they get overlooked.

GPS trackers are often installed at the behest of automotive financing companies in high risk cases. And no; if you find one installed and it doesn’t belong to you, you do not have the right to destroy it as it belongs to the lien holder of the vehicle and probably violates your contract terms.