Ok, so apparently they are real, but those pics are all over the web so i think the ad is a scam. They are pygmy marmosets. They only get to about 5 1/2 inches
One of my herp shops also deals in various primates. It may be different for other states but the license here in Florida needed to own a primate is 1000 bucks.
Primates are cool pets, but they require constant attention daily. I know some people that have them and they are stay at home moms and they are out with them all day long. Otherwise they get really mean.