I was just in a chat with Samsung, who was expectedly useless in my scenario. They told me my S7 Edge is worth $300 provided that there is no major damage, it powers on, holds a charge etc. I told them I opened the back (I had to replace the battery myself) and they kept telling me as long as nothing is cracked it's eligible. Problem is, there is this nice little line that says "including but not limited to:" before they list all the requirements, which means just because they don't list the fact that the user opening the phone could void the deal, they may still consider it. So if for some reason they deem it ineligible, I don't get the phone back and I have to pay $275.