This is a good question. According to the the American Marketing Association website, they have approved of the following definition of marketing.
"Marketing is the activity, set of institutions, and processes for creating, communicating, delivering, and exchanging offerings that have value for customers, clients, partners, and society at large."
As to your second question, marketers can do several things to deliver the best value to their customers. First, marketers could be honest and give customers only products that are built to last. In other words, they should seek to give customers products of quality. Second, marketers can look for the best deals out there, so that they could save the customers some money. In this economy, this point is very important. Finally, marketers can seek to market products in a cost effective way. This point is also worth mentioning, because marketing costs money and ultimately this cost is given to the consumer.