Frugal and Energy Efficient Living

That you measured the temp of the body of the water heater right next to where the mechanical water thermostat mates to the body of the water heater to make sure the t-stat opens within a reasonable range of the temp you read and you do that for both the upper and lower thermostats. I can put an adapter on my Fluke meter on which I can then hook up three different temperature probes. One for liquids, the other for air and the last for checking surface temperatures. And also make sure the wiring is correct by checking to ensure only one t-stat is closed during a call for heat at a time. I'd also would have done an amp draw check on the water heater when first one thermostat and then the other is calling for heat and I'd check the temperature of the hot water coming out of the faucet nearest the water heater after the t-stats on the heater are satisfied and open.

The main point of your OP is excellent. One can barter one's skills and time in exchange for something you need and thus save money. By doing what you did, you not only saved your neighbor a good size chunk of cash but you saved yourself a bunch too. As you said, it was a win-win situation.