Both parents should be fully health tested, not just eyes. You can see lists of what tests are necessary here for the miniature schnauzer and here for the miniature poodle.
Obviously hips and eyes are the most important but I would expect any breeder worth their salt to have done all relevant tests, including DNA tests where the conditions aren't common between whatever two breeds they're crossing. Whilst it may be impossible to produce affected puppies they can still produce carriers and they really should be aware if this is a possibility or not by fully testing both parents.
There are some health conditions shared by both breeds which currently can't be tested for so the breeder should have done their research and be as confident as possible that none of these (or any others) are lurking in the lines of the dogs they have chosen to breed from. Again, they should be happy to chat about this with you.
Expect to be thoroughly grilled by the breeder. They should be asking things like what your lifestyle and living situation is like, why you picked that particular cross, why you picked them as a breeder, what you feel you can offer a dog, etc. It shouldn't be a case of being able to see the pups and either leave a deposit or walk away with one with few questions being asked.
I would normally ask a breeder why they chose to breed from their bitch, why they chose that particular stud dog, what they were hoping to produce with that mating, what their long term breeding goals are. I also want to know that a breeder will offer lifetime support, including either taking a dog back (or at the very least helping to find a suitable home) if for any reason I was unable to keep them any more.
The litter and mum should be inside with the family, not kept outside in a kennel, and there should be evidence (such as a whelping box set up) that this is how they're kept all the time and they haven't just been brought inside to meet a prospective buyer. The breeder should be actively raising the puppies, not just leaving mum to get on with it herself. There's all sorts a breeder can be doing before the puppies go to their new homes which helps maximise their chances of going on to be well rounded adult dogs. This site breaks down the developmental stages of puppies and lists what tasks that should ideally be done during each.
Finally ask about feeding (what they're feeding, how much, etc.), worming schedules and what their plans are for vaccinations. Some breeders will get the first jab done but there can be issues with completing the course if your chosen vet uses a different brand of vaccine. Ideally if they've had the first jab done they will have a voucher for the second at their own vets so there's no issue or the pup won't have had the first one done yet. The breeder should also have plans to get the puppies microchipped prior to them going to their new homes, this is now a legal requirement.