How do you know if a breeder is a scammer?

My mother, a breeder, has many unsold kittens, all grown up. She once stopped selling kittens due to a family tragedy, but now, when I try to help her sell them, I encounter clients who are unsure about the cattery, wondering how it's possible that so many kittens are available.

What would you recommend to improve the legitimacy of the website/communications?