Normally, if we suspect a binary switch we do like you did, jump it and if the compressor kicks on (assuming you have a charge in the system) you know it's the switch.
I don't know the shop, but it is possible they didn't want to diagnose a system someone else installed. We get similar feelings when someone brings us something they put in and want us to fix it. It's hard not knowing how something was installed, most people we deal with are trying to save a buck and we end up having to redo nearly everything.
Not saying you don't know what you are doing, just giving a shop's perspective. Sometimes it's a simple fix, like a switch, sometimes the person didn't follow instructions and you spend 3-4 hours going through everything to make sure it's correct (wired directly to battery, no scotchlocks, etc etc)
Who knows, maybe they just had time for a recharge but not for a diagnosis!
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