chihuahua puppies i am thinking of getting

I went to look at the puppies yesterday and there are 2 girls and 1 boy.
The girls are a good size and the boy is considerably smaller. I asked if he was the runt and the man did not know.
The puppies are only 1 month so at 8 weeks he could grow bigger.
My question is: should his small size worry me or is he just smaller cause he is male, as i was told yesterday.
Thanks

First, the puppy is not smaller because it is male. Most likely it is the runt of the litter. Second, if the guy can't answer questions correctly, are you dealing with a BYB? Third, this little pup should not leave it's mom until 12 weeks of age for socialisation and bite inhibition with his siblings and mom. Fourth, run in the opposite direction from this person as he's not sounding very reputable. Fifth, as the runt of the litter, this pup could have more health issues later on which can happen often with the runt.