Actually I believe in science and consulting with an expert, but the friend with the 500 gpm did use a douser and it worked out for him.
He knew the property he had purchased has potential for artesian flowing wells but the first two wells came up dry. Although he was sceptical he decided he didn't have anything to lose and the two spots the douser pointed out worked.
Doesn't mean there isn't any science to it.
As far as opinions you know what they say about them. I'd rather get someone who has expertise in the area. Could be alot cheaper.