I will probably stay with the breeder. The fact that he called to discuss the situation and wants to verify what the other customer received and rectify the situation for all parties shows that he has customer service and will stand behind the animals he produces. Mistakes do happen sometimes. I once threw a male fancy mouse into my tub of grow out females by accident. That put my selling of pet mice on hold for a few weeks because I couldn't guarantee that a customer wouldn't magically get a litter of mice from the one pet mouse they bought.
Usually if I get an animal as a pet I won't bother verifying the sex but if I plan to breed it then I will verify.