RedRaz, did they look healthy originally when you got them? This is why I'm nervous about buying in big pet stores. :/
I thought they looked healthy. Then again this was the first time I ever bought and cared for a betta. So I could of missed certain signs. :( Look to see if you see any signs of illness like fuzzy stuff on fins, really large eyes, torn fins. Not to say that you can't care for these ill ones and bring them back to health jsut takes a lot of care to do so. Mine were too sick to be saved unfortunately. Not all are like that though. Just something to think about when buying a betta from a pet store. I would also ask the employee you mentioned when they get new bettas and perhaps she could call you when they come in. That way you have a better chance of getting a healthy one.
My Bettas: The Great Bambino *Babe* my big boy Marbled PK, Rosie my dainty Crown Tail gal ,my little HMPK guy Ginger Baker, Slash my Reptile HM male and my HMPK sweetie Sterling.