Please be aware of online scammers "selling" Maine Coon kittens. They might post cute photos with a name and add a link to "BUY THIS KITTEN NOW" for $500 or other too good to be true price.
Is the "Maine Coon" website advertising several breeds? Is the kitten living elsewhere? They could be a kitten broker (basically an online pet store). You will probably never meet the breeder or the kitten's sire and dam.
If you visit a cattery page and they do not mention anything about health screenings or health history, be very suspicious.
If you visit a cattery page and they have established their business in the past 2-3 years, who is their mentor? Where did they get their cats? It's unusual for a new responsible breeder to suddenly have 7,8,9 cats. Most new breeders start slow and gain experience. Is this relatively new breeder charging exorbitant prices? (Double what reputable experienced breeders charge). This is just something to think about. Having said that, there are plenty of very good new breeders out there. Ask lots of questions.
What about catteries that state their cats are from Eastern European and Russian lines? This is a native American cat breed. Those blood lines are NOT better. The cats have been bred to look completely different than our beloved breed. Most do not meet American standards. Just something to consider. Having said that, there are some awesome European breeders who breed for the correct look.
Shop around. Buy from a responsible reputable breeder who is focusing on health, socialization and breeds their kittens close to the standard. Both CFA and TICA have a written standard that American breeders should be striving for.
Good luck with your search.
3 lovely kittens bred by Fog City Cattery.