Never take the employees word, unless they really show off some real betta knowledge!
It figures one of the females is a plakat. However you might want to be careful, sometimes females just resemble males at time. Especially ones that are... "larger" (hehe).
Sooner or later, I'm pretty sure you will see some nipping, just for the sake of some... pecking order? Not sure what the term is. However, this is the "harmless" *or rather, 'be careful and cautious' part of it*. And it seems that just by living in captivity away from others doesn't tend to translate into them being more docile and less agressive. If anything, it would hardly effect it. Sorry to bring your happy mood down, but I just wanted to say!
Also, this is why (although it is not mentioned that much anymore, which it should be...hmm) it's recommended to quarantine all of them in a cheap little critter-keeper to watch out for ick or any other type of disease. Unless you are willing to treat an entire tank anyways. And chances are, your betta will be affected by disease sooner or later, just by being in that little cup. Looking healthy is not being healthy, which is why I add aquarium salt at the start for 10 days for my friend's fish. And especially if the employee doesn't look, might as well throw that 'info' out the window!
But hopefully, NONE of this bad stuff happens to you! I'm always the doubtful type, don't mind me! Haha. Can't wait to see pictures!