akane - I hope you haven't bought from any large scale breeders (or small scale for that matter, who don't like to admit to wholesaling because of pet folks who get outraged) who are members of MCBA or ECBC. If you did, then you are most likely buying from irresponsible, out for profit breeders.
Here is the reason you should not (though many do) get your breeding chins from a pet store. The wholesaler comes to the breeders barn and says I need X amount of chins. The breeder starts going through his/her cages and pulling animals that no one wants (standard after standard after standard) because they aren't flavor of the month. If they have a contract with the wholesaler, then they have to pull any and all animals they can to fulfill it. That means pulling kits from top showing animals if necessary. I once had a rancher tell me that someone buying from a pet store may have the next National champion because he had to pull from his top show chins to fulfill a contract.
The wholesaler then takes 100s and 100s of chins back to his barn and parcels them out to whoever he has a contract with - Petco, PetSmart, etc. Do you really think for the amount of money he's making that he's going to take the time to provide pedigrees with all of those animals? Of course not. Nor would the breeder selling them to him. Do you really think that PetSmart or Petco would provide a pedigree that tells you where the chin came from? Think about that. If they did, where would you go to buy your next chin? It wouldn't be from a pet store.
So it would be very easy for you to be breeding brother to sister, mother to son, etc. I have been breeding for going on 12 years now. I still won't line breed. If there is a hidden genetic defect (and NO breeder can claim to have a herd of animals with absolutely 100% defect free animals at all times) you could be locking that trait in because you just combined the two together. Why do that? If you want breeding animals with pedigrees, go to a breeder. If you want a pet, go to a pet store.
I realize that new breeders feel compelled to make derogatory remarks to those who have been in the business for many, many years and for whom it IS a business, but you should really be aware of your facts before you comment.
BTW, JAGS started their herd with a pet store chin. I believe it took grand show at Nationals. Something for you to ponder.