Maybe, Radhanath was just in the wrong place at the wrong time - he did move around alot and saw alot of Jimmy Hendrix If you read his bio (he is still alive) he has done a lot of good works/organizations
The reason scam guru's can exist is answered in the first part of your sentence.
I agree with newmedman that in the end gurus are basically, in the long run, only there for those who have trouble thinking for themselves. Personally, also, i think who as often as not are into scam.