I prefer solder and heat shrink with sealant when I do wiring repairs. Not always possible if you don't have enough wire to splice together and put heat shrink onto (without the heat shrink shrinking from the heat of the splice).
I don't pull other people's problems. On the rare occasion a customer hires me move their trailer i give it a very good inspection and if any defects are found they get it fixed while i collect detention. Now something as simple as a quick wiring job, I'll ask them if they want me to just do it, and if so i will do it just as good, if not better than i would my own. All depends on that specific customer and my relationship with them.