If you reserve a convertible at SFO, here are the possibilities:
60% - you get a Mustang
30% - you get a Camaro, and they'll readily swap it for a Mustang if you ask
5% - you get a Camaro, and they can't swap it for a Mustang
3% - no convertible at all, you're SOL
2% - no Camaro or Mustang, so you get a Mercedes convertible