Voltage Regulator problem

Small update and a problem/question. I straightened up the harness and zip ties it up. Didn't rewrap it in case I need to work on it again. Will rewrap after a few weeks. Took it back over to the parts store to have them test it again. On my multimeter it is putting out 13.5 volts at idle. On the parts store tester it is only showing 12.3 volts at idle. Also said the voltage regulator is bad. I'm inclined to trust my meter more on the voltage but am at a loss for the V/R.