There are some tricks to manipulate the mind of the consumers, which can be utilized by not only ordinary sales person, but can be used by larger firms. Although they are used unknowingly, there is no set list.
Mutual exchanging is the first and powerful trick. The company can start with giving something for free to the customer. He will take it for the first time, but from next time he will feel obliged and will try to return the favor. Offering the product for free initially can do this. And if the customer is satisfied with the product, he will buy it for himself from next time. Some salespersons get confused with this principle. For example, it is ineffective and wrong according to this principle, to quote 'Spend over $25 and get a free t-shirt'. The offer is not free; the customer has to spend something to get the free product. The product being given should be totally free without any condition to be fulfilled. For example, the line 'Get the latest lipstick shade absolutely free' will do the trick. If the shade is really good, they will buy it the next time and might even think of buying other shades of lipstick.
The next trick is to present something as of high value, but the company should incur only small or no amount in producing it, like information. It can tempt the customer by saying that the information provided to them is a big time secret and is not known to anyone at all. But some mess it up, by saying that they are providing very valuable information, but it turns out to be another advertisement.
Another example is giving out free sample to the targeted customers. Again the mistake made here is that companies distribute samples of poor quality or rejected products. This certainly lowers the customers liking towards the product and he will assume that's the way the product is actually and won't go ahead to buy it.
Use words, which initiate immediate action, like 'Limited time offer', 'Offer ending soon', and 'Offer till stocks lasts' are really motivating. The customer gets the impression that the offer will end really soon as the products are limited edition and he should go out and buy it at the very first chance. This works well specially with customers who have an interest in collecting antiques, collectibles and anything which are not easily available.
Tricking the customer in making a commitment is another next good method to increase sales. The trick is to make the customer to take small steps toward the goal, without realizing about it. Like when the customer requests for some information, provide them with the relevant information for free and make them fill a form and take contact information from them. This is like committing to get offers and information about products in future. Do not advertise in this step. In the next step advertisements about products and services can be sent to the customer to the address provided by them. Conducting surveys is another example.
Lottery is another good method. When a person buys a lottery ticket, he fills his address on the ticket. This information can be used to contact the customer in future. In the above practices it's very vital to not to advertise in the first step. Only after getting the customer contact information, should promotional mails be mailed to him. Long advertisements that are featured in the newspaper are a small twist to this trick. If the customer invests time to read the whole advertisement, he has committed and will surely respond to the ad.