Reputable vs. Nonreputable Breeders, Standard Things a Breeder Should Do

Not let kitten s leave until at least 12 weeks of age
Fully vaccinate their cats, not just the kittens
Provide you with a contract, that guarantees the kittens' health for a period of time, has a no declawing policy and an indoor only agreement. Additionally, it should clearly state that at any time if you can no longer have the cat/kitten, they will take it back, no questions asked.
Not let you take home a kitten who has ANY signs of illness, not even a runny nose!
Test (and be able to show proof) BOTH the mother and father of the kittens for standard conditions that can exist within the breed. HCM and Hip Dysplasia are frequently tested for in the Maine Coon cat. HCM testing should be done BOTH via DNA testing and echocardiogram. Breeders should be breeding DNA negative cats at this time. Ask to see the results of the parents' testing!
If they tell you that either of the parents haven't been tested because they haven't become "of age", then they also aren't "of age" to be breeding (although some don't test the cats' hips until 2). Testing is essential and this is one corner breeders should not cut. Also be careful that the ALL of the breeding cats are being tested and not just a select few. Most breeding cats are tested once per year or every other year.
Give you a pedigree and registration papers, even if the papers follow after the spay/neuter of the kitten
Require you to spay/neuter the kitten if not done so previously
If you are getting an adult, he/she should already be spayed/neutered.
Want your information, or questions you, about various situations of your life. These kittens should be like family to the breeder and they should want to know about you as well. Remember, you aren't just buying a new car.
They should own (and possess) the mother of the kittens. If not, ask why. If "friends" own the female, yet they have the litter of kittens, something fishy is most likely up and we don't recommend you consider a kitten from this sort of situation.
Show (or have shown) the parents in a major cat association on a regular basis. This verifies that the parents fit the standard set forth by the cat association for that breed. If a parent has not been shown, they should have a VERY good reason why and shy/poor temperament cats should not be bred because they can, very possibly, pass on this trait to their off-spring. A cat's temperament is just as important, in our eyes, as their health.