Very wrinkly/loose skin horizontally along body...

[Penultimate]

Is it digital or analogue (I think accurite makes both so I want to be sure)? You want the digital one, and you want to make it's in a place where it won't get splashed by the water bowl and double check that it hasn't just been peed on. Other than that, only way to tell if your equipment is faulty is to test with with a control; put it in a place you 100% know the humidity of or put it next to equipment you know to be accurate and compare readings.

If you missed the pink belly or blue phase of shedding it might be very hard to tell for sure, but over all the scales will just look dull and colors sort of washed out.

I'm not sure if too high humidity can give a snake saggy skin, someone with more experience there will have to weigh in on this.

High humidity shouldn't give a snake saggy skin, at least, not from what I've seen. I live in a humid area with my snake room generally being 50% humidity or more. I do what I can to lessen this, but every once in a while the weather gets ridiculously wet and there's nothing I can do. I haven't noticed any issues with saggy skin during particularly humid weather.