Spirit has a very, very cynical business model, and you really have to have your guard up. They'll borrow from other industries, even, such as with the "optional" Passenger Usage Fee for booking online rather than at the airport (seems silly, but it's a page out of Ticketmaster's book). Auto-renewal is borrowed from magazines and others and tries to turn an "opt in" into an "opt out."

In other words, assume nothing when it comes to fair business practices...the reason we need and sometimes get regulations (such as the new truth-in-price-quotes ones Spirit has been resisting) is because of bad actors that constantly try to rewrite the rules of the road to their favor. Too often it's the letter of the law rather than common sense that's the lower boundary for practices. Assuming otherwise is not a good idea.