
If other breeders are testing and this one is not... then I think I would be going with the 'other breeders are more responsible than this one' line of thought.
There are one or two conditions, one I can think of in Deerhounds, where its not quite so black and white..
Factor 7 deficiency - its not life threatening, its unlikely to ever be a problem and its been around for YEARS before we either knew about it, or could test for it - however, now we DO know about it, I think it would be irresponsible of breeders not to KNOW the status of their dogs.
I would personally (which is easy for me to say as I don't breed) not actually let that information heavily influence breeding decisions - but I do think breeders should use the tests available and be transparent about the status of their dogs (ie, affected, carrier, non carrier) so that we all know what we are dealing with.
I do think there are very very few conditions like this though and anything that other breeders are routinely testing for, that would affect the health and lifespan of the individual dogs produced, should be tested for and those results used in the careful consideration of who to breed from.
A breeder NOT doing this gains what exactly? A false sense of 'pride' that certain conditions are not proven within their lines.. A hefty saving in time and money.
Neither of these things are to the benefit of potential puppies they produce, or their prospective owners, so I would probably walk away here!