Companies that only give you copies of the list of things they cover AFTER you sign up with them?

Does anybody else have these experiences, whether it's gym memberships, or other companies that provide services, whereby they don't give you a written list of the services offered in your plan until you buy it? The only way of knowing what is covered under your plan is to talk with the sales representative. How do these companies get away with that?

Companies that only give you copies of the list of things they cover AFTER you sign up with them?
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