I think using the OFA website is a good research tool as you will often get answers right away as to whether a breeder does truly have their dogs checked. But many do not submit results and asking for the certs and asking about the breeder's approach to breeding is always the most im[ortant thing to do.
Also I find the OFA site useful as if absolutely no dogs from the breeder's kennel name comes up, then I would want to double check they are a legitimate show breeder too. Usually even if the breeder might not send in results, others who own his or her dogs may have. You can also use the breed pedigree databases online to do this kind of basic search. Newer breeders of course may not appear in any such results but again, then you want to be sure to talk and ask the breeder directly such important questions as that is more imortant than internet results. Also few breeders outside the US/Canada use OFA.
Every good breeder I have ever talked to is VERY happy when prospective buyers inquire about their lines and breed health, and any testing that they do.
Some may or may not do some specific tests and they should be able to discuss why not. I don't know any good breeders who wouldn't be cardiac testing, however, for example. And personally I'd prefer breeders who do use testing to be as aware as possible of the status of their breeding dogs.
There are different perspectives amongst breeders on which tests to do and how to use results.