How do they use bias to sell their products ?

Well, I'm not sure who's doing the selling but many companies will use a bias to sell their products. Think about commericals, you rarely, if ever, see negative feedback on the product itsself.  This is because they want people to buy the product BECAUSE someone else said it was great.

you must remain stopped until the stop signal is retracted and the red lights are turned off. approaching traffic in the opposite roadway of a divided highway shall not be required to stop, even if the school bus has the stop-arm extended and the alternately flashing warning signal lamps on.