How did you find out they were being WC instead of CB?
The prize of $15 seems like juvenile CB, WC adults would most likely be higher prized.
At least around here, WC frogs are more expensive then CB frogs, now they are CITES listed you need to become a CITES number with them when they are WC as well.

Besides, you mentioned the offer he did. Giving back money on 2 out of 3 frogs.