How can you differentiate between cross selling and up selling ? which one is easy to achieve?

Cross selling is when your customer is already set to buy your product but you make an additional sale by introducing another product that completes his purchase, for example selling a Home Theater sound system to a customer set to buy a TV. Up selling is when you switch the purchase of your customer from the product he was there to buy and convincing him to buy a more expensive one, for example switching a customer from buying an entery-level LED TV to buying a mid-level3D TV, and that happens when you introduce the extra features and benefits from spending that extra money. Neither of both methods are hard to be achieved, but it all depends on the customer ability to pay more, this should be the sales person's job to be able to know such info in a smart way during his conversation, also the deep knowledge you must have about your products, which makes highlighting features and benefits an easier job.