From an author and sales trainer's perspective, let me disagree--somewhat.
Most of the other authors and trainers I know don't think their training is the only way. Most will quickly admit there are alternatives and most will refer to other authors and trainers if they don't have the right training for someone. My specialty is referral and other sophisticated lead generation methods and personal marketing, but I refer people to Wendy Weiss for cold calling and phone communication skills; Dave Anderson for auto sales training; Dave Lakhani for persuasion training; and many others. Others do the same--I know, because they refer many to me.
A perfect example is Frank Rumbauskas. Frank is the New York Times bestselling author of Never Cold Call Again. Last week his newest book, Selling Sucks: How to Stop Selling and Start Getting Prospects to Buy, was released. It discusses a number of sophisticated methods of generating high quality prospects and converting them to clients. One of his chapters is on generating referrals. It's one of his shortest chapters because he concedes that the best book on the subject and the best training on the subject is mine--so instead of repeating what I say, he advises his readers to buy my book and take my training. That's hardly viewing his training as the only training worth taking. But on his website, he makes a very strong case for buying his books and taking his training--as he should.
There are some who will claim to be the be-all and end-all of training. But those are the exception rather than the rule.
However, when marketing our training and other products, most of us do make strong statements, of course. We are selling a product, just like you are selling a product. And most, at least most of the good ones, are true believers in their training. So, if you truly believe in the value and quality of your training, why wouldn't you make strong statements? And, since most of us have endorsements and testimonials from salespeople and business leaders, we let them do the talking for us by posting their testimonials on our websites.
It's not so much the trainer who is a strong believer in his or her training that you should watch out for, but the one who is lukewarm about their training. If they aren't sold on its value, why should you be?