What's wrong with "sell"?

There are a *lot* of adverts on the TV right now for services like MazumaMobile, mobilephoneXchange and various others. There is also CashMyGold and PostalGold and no doubt many others. These are all companies to which you can sell your goods. The one thing that all of their adverts have in common (apart from being insanely annoying) is that none of them use the word "sell". I really can't understand why.

The most commonly used wording seems to be informing people that they can "exchange" their goods for cash. We already have a perfectly good word which means almost exactly "exchange for cash". Why don't these adverts use it? Because it would remind people that there are various other routes through which they could sell their gold/old phone/whatever? Because the word "sell" is unsavoury?

NB - Mazuma goes even further, suggesting that they can 'magic' your phone into cash... imagine that!