I've come across this topic many times and would be good to learn and read about real world success experiences on how consulting/software development companies are successfully selling its services under agile and what strategies work the best. One of the major concerns to overcome is the complexity to arrange a contractual agreement that accommodates change (let's say client is coming from a waterfall approach) since he is going to want to know how much the project will cost, and when they can expect to receive working software as done in fixed bid contracts.