Be sure the repair guy knows that the RV wiring is tad different than regular house wiring. Use this chart for your 30AMP wiring check. Make sure the readings shown here can be duplicated between the ground and neutral readings...
This is typical camp ground PEDESTAL wiring setup...
This is what you read when measuring around the 30AMP/15AMP/20AMP Pedestal receptacle.
Then also use a standard CIRCUIT TESTER plugged into the 30AMP Receptacle using an RV30A-15A Adapter (WALMART). Use this chart for proper lights reading.
If the repairman cannot duplicate these readings then DO NOT power up your trailer using the shore power from that pedestal setup.
Just my thoughts