I know a number of surveyors that do stand by their work, what none of them really can do is insure they didn't miss anything. There are just too many places that a hidden defect could be that you just can't get to without destroying the boat.
I have been sailing since i was 2, working on boats since I was 12, spent years working in a boat yard, then on a big budget racing program, and now work in maritime law, I have even helped some commercial surveyors in the past. Yet when I bought the new boat I got a survey and he found things I missed, but the guy we used is a professional who works at his craft. On the other hand the guy you delt with sounds like a quack, and in my eyes should be personally shamed.
I would get in touch with SAMS, and BoatUS, and any other surveyors organizations and file a complaint about this guy. Missing a hidden defect buried in the bilge is one thing, miss counting how many and of what type of extinguishers is another completely.
If you know of a surveyor who will legally stand behind his work, name him.
If a surveyor were to say that he checked out something in particular, but was unable to confirm a certain item or area for what ever reason then he should state that individually in the report, but that is not what they do.
They cover the entire document with a declaimer that states they don't stand behind any of it.
Who am I going to file a complaint with? Like all surveyors, he has put a disclaimer on the survey report that he is not to be held responsible for any of it. An "Attorney" should know that because of this disclaimer there is nothing anyone can do about it. Therefore, it's a useless piece of paper that leaves you with no recourse.
By the way I live in Canada.