The invention provides sampling, escrowing, and other tools and techniques for facilitating transactions that involve digital goods. Transactions may be of the goods-for-payment type, or they may be barter transactions that exchange goods for goods. Digital goods may be escrowed with an automatic broker....http://www.google.co.uk/patents/US6343738?utm_source=gb-gplus-sharePatent US6343738 - Automatic broker tools and techniques
