
Hmm, I would totally accept it and resell but I honestly don't have space for 2 tanks to be delivered in the next week and then sitting on it until it sells..Yeah, because of what @Jessican read on their website: The guarantee only applies if you purchased from IM directly, not from a third party. It sounds like you ordered through BRS. So, you’re either stuck with the tank or stuck with having to pay this cancellation fee.
Like @AlienReefer did, your best option might be to try to resell the tank locally.