A very common term in contracts is what is called a merger clause, and what it says essentially is that the contract forms the entire agreement of the parties,

A very common term in contracts is what is called a merger clause, and what it says essentially is that the contract forms the entire agreement of the parties, and that any oral representations not contained in the contract are irrelevant and to be completely disregarded. But there are courts that hold that a merger clause is not absolute and has its limits. There are also places, like here in the UK, where statutory consumer rights law explicitly says that trying to hide behind those clauses doesn't stand up. You can't have a salesperson answer a consumer's questions about a product, and then when the consumer finds the product doesn't match the information they were given after buying it, argue that your Ts & Cs say anything the salesperson said before the purchase has no weight. Moreover, if you make a habit of trying, you're likely to attract not just action by the consumer themselves but also the attention of regulators who may be considerably more powerful than any individual consumer.