2. They offer BTC acceptance as a side option. In other words, It's just an exchange service between BTC and USD.
They can't offer this option. They have no right to do this! To be "just" an exchange service you have to be "just" regulated as an exchange service... like MtGox, for instance!
CASE1. Merchant originally accept 1kg gold for 1 computer deal.
CASE2. Merchant originally accept USD for 1 computer and they have an additional service which is "Take some gold and exchange it to USD"
CASE3. Merchant doesn't sell you anything. Merchant just accepted your gold as a guarantee for PRE-ORDERING something!