If a company makes unambiguous claims in their advertising which turn out to be false, they will get sued and maybe even fined by regulators. Much of the world does in fact operate on this kind of trust.
Firewalls solve problems like this. Relying on a secret callback mechanism to run your business is high risk, when you have sophisticated customers. A number of industries have low risk tolerance and default deny traffic, which would make those industries inaccessible to a company that tried to operate that way.
