If you are looking for a dog to compete in any of these categories, it would be wise to find a breeder who also enjoys that activity. They may also use glucose strips to check for Fanconi Syndrome or have a DNA test for Hemolytic Anemia. A good breeder will be willing to show you the results. Avoid breeders who claim that their dogs have no health problems. Responsible breeders understand this and make an honest effort to breed intelligently to produce the healthiest animals possible.
Most responsible breeders do.
Get it in writing. A responsible breeder welcomes visitors into their home. Keep in mind that most breeders work full time, have families to raise, and attend dog-related activities on weekends so setting up an appointment to visit may be a bit difficult. If you do set up an appointment, please be on time and if you aren't able to make it, contact the breeder and reschedule. Avoid anyone who refuses to allow you to visit or who wants to meet you in a parking lot or on the side of the road to sell you a puppy.