Everyone wants to charge based on the value you can bring your client.<p>But, based on my experience, it depends a lot on your client and business relationship with them. If you have a good relationship with a client, you can generally get a sense where their finances and business trajectory is. When the big estimate comes, they're okay with it because they know they'll get the results, and finding someone else has huge opportunity cost for them (the devil you know). And, the opportunity cost of finding someone else would be astronomical if it's an emergency.<p>So when your next agreement expires, just up the price to whatever you think is fair for you, you can even just come down on price if it looks like they won't close. Plus, emergency response is a huge inconvenience to you, so that should cost big time. Personally, I would create a separate fee structure for it, and of course a different line item on my invoices.<p>Whatever you do, just remember that it's a business relationship, and relationships go both ways.