1. Before you talk to them make sure you are clear about your goals and strategy.
Outsourcing any part of your business or hiring a firm to do work for you should be like hiring an employee. You should have a VERY clear idea about what you want them to accomplish. After all - you're hiring them to help you accomplish your goals... not defaulting to their strategy to accomplish theirs (remember - they are a business too).
2. Before you talk to them be certain you know what your reasonable Customer Acquisition Cost (CAC) is. This is the number you'll use to know if you can afford the services. When discussing pricing - don't mention this to them - let them TELL you the costs of their services. But knowing this will allow you to decide if you can afford the investment.
3. Find out what they do to mitigate risk for their customers. In other words - what are they willing to offer YOU to ensure YOUR success. If they want a lump sum payment that's non-refundable... run for the hills (unless they offer some other amazing guarantees, etc.).
For assistance figuring any of the above out - or for any other help - give me a call.
Best of luck!!