They're supposed to be quite competent in the fields where they evalutate patent-applications.
They'd have to be, afterall, because the chief criteria are first that it's novel, and second that it's non-obvious. The definition of the latter vary somewhat by jurisdiction, but for USA it means that:
"the difference between the subject matter sought to be patented and the prior art are such that the subject matter as a whole would have been obvious to a person having ordinary skill in the art to which the subject matter pertains."
In other words, if the technique being patented would have been obvious to a person who has knowledge of formerly used techniques *and* ordinary skill in the subject-area, then that technique is not patentable.
That's what the law says - offcourse in practice it doesn't work like that. It *is* obvious to a person of ordinary skill in developing payment-solutions for webshops that shopping can be made with one click if the required information has been stored previously - and it's equally obvious how to implement this. Nevertheless the patent was granted.
A patent-examiner, in principle, has examined the application and determined that it is novel, non-obvious and useful. It's gonna be really tricky to make it stick that believing his conclusions amounts to criminal neglect.
If you *could* make it stick: "Nobody in their right mind could believe this", then you could conceivably also sue the patent-office for criminal neglect, since they'd be guilty of the same mistake.
That'd be the day -- but I ain't holding my breath.