That statement is true,
By examining the sales person's facial expression you could spot which words that come out from their voice are sincere.
If the sincerity is spotted when the salesperson is asking for the problem that you have and the solution that they give, they might genuinely believes that their product might help you.
Railroad, barbed wire and the modern water pump
Answer is in the photo. I can only upload it to a file hosting service. link below!
tinyurl.com/wpazsebu