Customers have an anti-persuasion forcefield. 

Even if you’re honest and your products are magnificent, the customer’s default position is to reject your claims. 

The way around this is to avoid having to persuade them. 

If a customer sees lots of your marketing over an extended period of time, and if that marketing is always helpful, you will gradually build trust with that customer and slowly neutralise their anti-persuasion forcefield. 

By the time the customer contacts you, you won’t have to persuade them, because your marketing will have already done that.