I love this game. It's extremely addictive and spent a good majority of yesterday playing it (thanks to the Steam deal).
However, I am not a big fan of the music in this game. I really just cannot get into it. It is possible to change the entire soundtrack to the game though. If you were ever curious enough to explore the Recettear folder, you probably already know, but I'm putting this hear just in case someone is searching on the internet for this answer.
Rename and save over the existing .wav files with the music of your choice and you just changed the soundtrack. I replaced everything with FFVII music. Happy haggling everyone! --- "After I die, you can eat my brain. It will give you power." -Duke Phillips psnprofiles.com/FrunDeatt66