If there's any rule that's true in business, it's that nobody likes when companies try to pull this particular move.
Every few months, business magazines and newspapers publish lists of "companies people hate." These lists always consist of same companies: banks, airlines, cable/telcom providers, and social networking sites.
Those are very different types of businesses, but they have one thing in common: they all tend to spring unpleasant surprises on the customer after the customer has bought their product.
With banks, it's the surprise of extra charges and fees; with airlines, the surprise of delays and cancellations. With cable/telcom providers, it's the surprise of incomprehensible bills with unexpected price increases. And with the social networking sites, it's the surprise of discovering that they're violating your privacy.
In all of these cases, you probably signed a contract (perhaps just by clicking through) that warned you that those surprises might occur. However, what you need to know was probably buried in pages of legalese. Who has time to decipher that?
Indeed, the companies in question are assuming and hoping that you won't bother to (or are unable to) figure out what's really in the contract because if they made it explicit, you might buy (or spend your time) elsewhere.
In other words, the "companies people hate" are trying to bullsh*t people into buying what they've got to offer. And people hate that.
What does this mean to you and your business? Plenty.
And if there's any rule that's true in business, it's that everyone hates unpleasant surprises, especially after being handed a line of bullsh*t.
So if you want loyal customers who sing your praises, always let them know exactly what they're actually buying before they buy, even telling them that that means that they might go elsewhere.
There is simply no more important rule in sales and, for that matter, in business in general.