Hi eaglesaquarium
Congratulations on your new corys. They look cute and perky.
It's not difficult to tell the sexes apart with mature pandas. There is a clear difference in size between the larger female and the smaller male.
One thing to keep in mind is that C. pandas like their water to be a little on the cooler side than many other tropical fish. With temperature requirements of 71 to 77 degrees F., they are usually fine in an unheated tank. They are not difficult to breed at the lower temperatures.
AquaBid is actually one of the best places to get interesting and unusual corys. The thing to do is look at the feedback and talk to the sellers before you buy. If anyone doesn't want to answer questions from a prospective buyer, they are not someone you want to have anything to do with. Also, I had a bad experience with Liveaquaria and would not recommend them to anyone.
BTW, what state do you live in?