1. Does the motor run at all?
2. Simple to tell if the motor is bad---You test for 12 volts positive at the cable to the stud on the motor and have someone activate the system IF NO 12 VOLTS, then look elsewhere. IF 12 volts and the motor does NOT run, then the motor is bad. Powergear the ground is the casing on some motors and on others there is a separate ground stud on the motor. Regardless, before condemning the motor, you apply 12 volts and ground to the motor and see if it runs--SIMPLE- If it does, the motor is good, if it does NOT the motor is bad.
3. Me thinks your RV shop lacks good diagnostic knowledgable techs.
4. Having the PG motor rebuilt is common if you have a local shop that does these. They rust out from water intrusion
5. IF the motor runs but no pumping, then I suspect they lost the keyway(shaft between the motor and pump impellor) when they pulled the motor. Doug