Sirius XM Radio review: Refusal to honor free installation promotion

after purchase of a vehicle without satellite radio capability, a representative of XM radio offered a promotional radio for $20 with free installation at any Best Buy installation center. I accepted the offer and upon receipt of the radio, I took it to be installed at the nearest Best Buy. After installation, Best Buy would not honor the free install card provided with the radio. I called the number on the install card and the agent told me that the cards are not honored by Best Buy outlets in Pennsylvania. Despite numerous calls to XM Radio, complaining of a promotion I accepted not being valid in my state, I was refused refund for my installation cost.