Parts-installer vs Technician

Parts-installer can remove any part on your car & reinstall it usually at a very good price. Example, a brake job or tune up for $20 or a pack of Marlboro cigarettes. They usually don't have updated diagnostic information for your car & if they're guess is wrong, they'll convince you that you needed that part too so you can pay for it. Warranty? "Oh. It'll be ok. Just call me if you have trouble."
Technicians are usually certified, have years of experience and/or dealership-trained. They have hundreds of hours of continued training and own updated equipment to diagnose your car. Warranty? "Warranty is on your invoice. 1-3yr warranty."
So who is working on your car, a parts-installer or a Technician?