It is sad that so many breeders don't take the problem of HCM in our breed seriously enough. Yes, it is a frustrating disease as apart from researching pedigrees (with which you'll have to rely on the honesty of others) and screening yearly (which doesn't guarantee the cat will remain HCM negative his/her entire life), there is not much you can do. No way to get any certainty until it is too late. But that is in NO way an excuse for not trying.
I have struggled with this issue a lot. I'm still struggling with it. Through reading, keeping track of forums and Yahoo-lists, talking with and asking advice from knowledgeable breeders I have tried to be as informed as possible before buying my breeding Bengals. The HCM-positive list is VERY helpful and I also have my own list. I do everything I can think of to minimise the risk of ever having or 'producing' a Bengal with HCM or any other health issue.
The age of the ancestors of my Bengals is also an important factor in deciding whether to buy them or not. I preferably look for Bengals whose parents, grandparents, etc. are 'older' and confirmed healthy.
The three breeding Bengals I have now all passed my 'health test' and also live up to my standards regarding character, body structure (no cow hooks, weak backs, weak joints, etc.) and appearance. It took me two years to find them, but it was worth it
And then my (our) stud Valentino turned out to be PK-Def positive... I (we) was gutted. He is truly the sweetest cat you can imagine. Gentle, social, cuddly, friendly, balanced and a great father to his kittens.
But at least it is an 'easy' disease. A DNA test gives a definitive answer about the status of the cat. If only that was the case for HCM.
To me, dealing with HCM is all about keeping informed, sharing knowledge, minimising risks (I feel it's impossible to completely eliminate risks) and common sense.
I always inform people honestly about the character and health issues of the Bengal breed. More often than not, I won't hear from them again.
Buyers have the power to change breeders' ways, but breeders are responsible. However, buyers are also responsible to make sure they are informed (and are willing to be informed) before buying.
EDIT: And yes, I screen my breeding cats yearly.