"
so I am suppose to believe a zapper salesman with no clinical study proving his product kills worms
"
The situation is worse than that : after all these years all he has provided is vague juggestions and vague testimonials (of users who have probably used several treatments at the same time) but there is not one objective proof that a zapper manages to kill parasitic worms (especially the big adults)
He has also changed the way he tells his story about how he got rid of a tapeworm, in the past it was because of a big dose of epsom salt, and now it is because of the use of his zapper.
His intent ? Probably to influence more desperate infected people to buy his product ?