Platy Gender?

[Hummingguppy]

I just went to the pet store to but I trio of platies, one male and two females. I know how to tell the difference between the anal fin, and in the petshop there were only males, as far as I could tell. None of the fins were fanned, anyways. I asked the petshop guy if they had any females, but he said that they only had what was in the tank, and seemed kind of confused. So my point is, is do females curl up there fin when stressed? Because the tank did look over crowded. And of they do, how do I tell the difference now?

 

[Old Scales]

I don't think they can fold their anal fins enough that you could not tell it from the male's gonopodium. IMO.