Declare the correct value on the Customs form?

Of course if it is "not as described", then perhaps $50 is an accurate value.

I don't know anything about customs but the above comments are spot on, fraud is bad on any level and if you got something that wasn't nearly as described, and you put a $50.00 value on it, your refund will be $50.00

what someone else said. You’re returning used goods. There should be no charge.On the other hand, what customs inspector is going to question a value of $50 for one LP? No LP ever made is worth $1200. They might be more inclined to question such a huge value. Then there’s your own self interest; you want your money back.

Ouch. I hope you can afford the loss on this, but it doesn't sound good. 

You don't even want to know my thoughts on this...