rat gender

So this pet place sells rats, and had told me a rat was a girl when it was a boy before, so we sadly had to exchange him for her. But we’re thinking it’s a he again, can anyone help? Are they a boy or girl?

Hi! I'm a new rat owner, and I just took home three double rex babies. However, I have no idea what gendrs they are. I'm pretty sure atleast two of them are males. I'd appreciate any help!