There are two assortments of Werneri that go to stores, the small ones usually are mixed sexes, but you can tell females apart by lack of long fins. the larger size ones are all-male assortments.
Another thing you need to know is that Werneris are TOUGH to keep long term. They always go through a sick phase when you get them, every batch I ever got had ick on them, but with good conditions and right food they recover quickly. Feeding them is not easy. They have tiny tiny mouths and most normal fish food is too big. I have mine on frozen rotifiers and dried cyclop-eeze which is their favorite food.