I don't think there is a 100% accurate method, but there are far more less than accurate methods than accurate.
Who says the person doing the skin-fold test isn't grabbing more skin than the previous person, and giving a far different reading? Or maybe you're blowing out all your air on the hydrostatic test? Lots of variables.
I know I've been tested at 5.7% using a skin fold test, but I didn't look like it IMO. So at that point I was thinking that the pros "must" be at 2-3% if what the magazines say is true!
In recent times I've been far leaner than when I was measured previously...does that mean I was at 5% or below? I don't think so.
That's why judges at a contest don't use what the person weighs or has for body fat % in their results.