They are probably right, it is more than likely the TRANSFER SWITCH.
Can you check it yourself? If you are comfortable with electricity, then yes. If not, then you might open it and look inside at the connections and see if there are any "burnt" or loose connections that could be tightened.
On ours, the connection was loose and it "arced" and melted a wirenut connector. We stripped the insulation from the cables, installed a new wirenut and haven't had a problem since.
However, I also wired my house, so am fairly comfortable working with electricity and using a volt meter....On our VEGAS the hardest part was finding the TRANSFER SWITCH (which was a large box with many wires going into it) It was not where THOR said it was, and not where the schematics said it should be. Turned out it was under the stove.
But, the scavenger hunt in trying to find it got us REAL familiar with where things were in the coach.