Free market of United States?

I learned this from my state government state's attorney general's office. United States is a "FREE" market so any and all merchants and/or businesses can make any rules (thoroughly and carefully) designed in their favor as long as it's not outrageoulsy ridiculous crossing the legal line subject to interpretation, and they can ask you to sign under their rules to proetect and guarantee their business' interest or refuse their business. Is this really how U.S.' free economic system runs and if yes how can you protect yourself as a consumer or a customer?