I would go sooner aswell if you can do that. How far away from you is the hamster? Did the guy give you a telephone number and his location? Check it on google maps to make sure it`s a true address (or royal mails postcode finder!) and then arrange when you can go and collect her.
As the others have said, they might not want to give out too much information purely because if they do so, like say that she isn`t good with handling or she bites, that may put people off, so they don`t mention it. They really advertise their hamsters because they can`t be bothered with them anymore. It`s as simple as that sometimes.
Hope you get her. x