I’m not sure if this really classifies as covert persuasion but it’s ceratinly about the psychology of selling.
You see as a salesperson it’s your job to meet people, get them comfotable enough to talk to you, then introduce a product or a concept they do not know and then help them convince themselves that this product/service will help them to such an extent that they want to buy it.
No mean feat.
And if you think that this can all be done with logical argument and following a set process, you have rocks in your head !
There is psychology behind the process. You are dealing with people and they all have their own values and beliefs and biases. If you want to succeed at selling you have to work with these factors both on the general level of the massess and on the specific level of the person in front of you during a sales meeting.
To help you get started on this adventure here is an article about sales psychology,