I show every prospective client any and everything they wanna see. As an installer, if you have something to hide than you're cutting corners. We pride ourselves with what the install looks behind the panels, dash, etc. It's all in the details. But if they don't want to show you, then maybe that's not a good thing.
Even if they say they solder everything, it doesn't necessarily mean it's good work. I've seen some jobs that are soldered and look like absolute crap (not to mention the solder was just a giant solder ball instead of "soaked" into the wire.