Wondering if the shop is buying cheap inserts and swapping them more often.

Man, I COMPLETELY disagree with that old timer! Light meters exist for a REASON, and throwing that tool away is like a carpenter ditching his tape measure because he "feels" the wood is exactly 4 feet. Your gut is great for a lot of things, but it's not a precision instrument, especially when you're dealing with tricky mixed lighting or you're trying to nail a specific look with slide film. If you're shooting Portra, sure, it's forgiving, but try that with Velvia 50 where a half stop off ruins the whole color balance. Your meter isn't "lying" to you, you just need to learn how to read it properly and spot when it's being fooled by a scene.

Wait, are you saying you never adjusted the base plate on your router to make sure it was perfectly flat against the bit? I did the same thing for years, but it was the fence on my table saw that was slightly off, not the blade angle. It took a guy at a cabinet shop showing me how to shim the fence with a business card to get dead-on cuts. Felt like a complete fool, but at least the fix was free.

Yeah, I'm not totally sold on this. There's a reason most people up north still use gas or oil furnaces. You're talking about one guy's setup and one winter, which could be a fluke. Maybe his old electric heater was just terrible or his house is super well insulated. I'd need to see a bunch of neighbors with similar houses and the same brand of heat pump to really believe it's that serious.

Yeah @jade_grant95's right, just give it time and don't toss it unless you actually see mold.