You can't see a warp that would cause this. If they just pulled a wheel and looked then if pads looked ok they will check it as good. The warp is developed because of the normal heat that builds up when braking caused by the friction. The more it is used the more it will warp and pulse, especially when slowing from highway speed, like on an off ramp.
If you have the rotor machined it will be thinner and therefore warp easier again. Thinner means it will not dissipate heat as easily.
Buy 2 new front rotors, quality ones, and install after cleaning the surfaces with brake clean. Check the pads and scuff with sand paper and clean them with brake clean. Clean & lube with correct high temp lube where the caliper and pads slides.
Reinstall everything and then go for a short drive and seat in the pads to the rotors. If the pads are thin then replace them before reassembly. To seat them apply the brakes a little hard when slowing from about 35-40 mph but do not do a panic stop. Do that about 5-6 times and should be good. Rear rotors could be warped and adding to problem but since the front brakes do most of the braking then they are typically the culprits.
