Exactly. Sounds like the feed store person didn't know for sure, and neither did you. If you wanted a guarantee, then that's something to work out with the seller beforehand. You also could have walked away when the feed store person told you they didn't know for sure. Caveat emptor, I'm afraid.You said the person at the feed store "guessed". Since neither that person, nor you, could tell what was what, I don't see that anyone cheated you.
Time will tell whether the chicks are males or female.