Our development shop would really like to do more agile projects but we have a problem getting clients on board. Many clients want a budget and a deadline. It's hard to sell a client on an agile project when our competitors do come up with waterfall-based fixed deadlines and fixed prices. We know their fixed numbers are bad, but the client doesn't know that. So, we end up looking bad to the client because we can't fix the price or a deadline but our competitors can.

So, how can you get your sales force to successfully sell a project that uses agile development methods, or a product that is developed using such methods? All the information I found seems to focus on project management and developers.