Whenever possible, visit the cattery. Are the cats caged, or part of the family? Are they well socialized and friendly?
They won't let you visit?......Walk away!
Ask if the breeding cats have been shown and championed. This lets you know the cats fit the written standard and you are getting a quality cat and the breeder is not just breeding to make money.
Having cats from Champion & Grand Champion lines is little more then a sales ploy. Same with Imported lines. If their cats do not have titles, find another breeder. Ask for names of other catteries they work with.
Reputable breeders have a good network of reputable catteries.
Does the breeder answer all your questions? A good breeder has nothing to hide is helpful & will answer any questions you have.