I am still missing something here!
First off, congratulations on getting your pet back! That was a horrendous blunder by the LFS employee(s) involved that it is totally incomprehensible!!!!
Something is as "fishy" (pardon the pun) as heck going on here. Not a snowflake chance in Hades that some kid that is a new employee at this LFS is working solo. Chances are that there was management/ supervisory level or at least senior experienced co-workers on site during the sale. If a brand new employee is running the LFS solo, then IMO it is not the new employees fault. It is your BUDDIES fault for GROSS MIS-MANAGEMENT!!!!!!!
I would think that the "new" employee would certainly have deferred the pricing question to their superior(s) with one MAJOR exception.
IMO the "kid"/ new employee "knew" the "customer" who purchased your RD and very intentionally made the sale under the radar of store management. This B.S. that happened to you was no accident! If the "kid" really was "acting on their own" then they are utterly retarded for NOT making the sale "under the table" and leaving a "legal" electronic paper trail of the sale to be easily tracked.
Either way, you buddy that "owns" this LFS has bigger problems than just your "incident". He/ She is being robbed and absolutely require better management in his/ her business!
You are extremely "lucky" that the "customer" that purchased you fish at this "steal price" was gracious enough to just "give it back"! You have to "TRY" to put yourself in their situation:
Supposing that this WAS on the up and up caused by a single new rogue employee, the customer is 100% free of ANY WRONG DOING! Why should they "the honest customer" be the ONLY ONE made to pay for the horrible injustice that was done to you (AND NOT BY THEM!!)? Getting your $15 back does NOT COVER THE "EXCHANGE". They may have driven many miles each direction and invested several hours of their time on this trip. I would not give a rat’s rectum about the Owners/ Managers inability to properly staff their store. That is 1000% not my frickin' problem.
I would be all about you getting your pet back that was erroneously sold to me. I would NOT however be willing to take ANY loss as an innocent in the matter. The LFS ABSOLUTELY must swallow the loss.
I am not a RD fan and know nothing about them, but if I purchased a 9" RD for $15 and the going rate for that fish is say $100 then I guaran-***-tee that I am going to want at minimum, $100 for the fish back, or a fish of MY CHOOSING which retails at the $100.