My Customer Service Rules

I've spent the last decade of my career dealing with customers, both directly and indirectly.  I've made my fair share of mistakes, and I also did a lot of things right.  Whilst I still have a lot to learn about customer service (I am technical, not sales after all) I also have some rules that I believe one should unflinchingly abide by.  These are, in no particular order:

1. Never lie.  Not to your customers, not to your colleagues, not to anyone.
2. If you make a mistake, be accountable.  Everyone makes mistakes and most people of worth respect and appreciate honesty.
3. The quickest way to lose the respect of your peers and customers is to point fingers and trying to apportion blame.
4. Get to know your customer and their business.
5. Listen.  Understand the problem from the customer's point of view, not just a technical one.
6. You expect to be paid like a professional, so act like one.  Do not become too "friendly" with the customer and do not swear in front of them. Ever.
7. "It's not my problem" does not exist in your vocabulary.  If it's not within your domain then help the customer resolve it by roping in someone who can.
8. Always notify the customer when you are about to make changes.  E-Mail is only sufficient if the customer acknowledges the mail, otherwise follow up with a phone call.
9. Only stick to the communicated changes.  If you tell the customer you're rebooting the mail server, do not reboot the file server as well.
10. In that vein, always make sure your customer does not get caught by surprise by always communicating updates.
11. Stick to your appointments - if you say will show up at 9 then you show up at 9.  If you can't then you let the customer know in advance via a phone call - e-mail is not acceptable.
12. Share your knowledge with the customer.  This will not make you redundant, it will allow you to provide value further up the chain.
13. You exist to serve the customer and their needs (within reason).
14. Speak to your customers often, no less than once a month.  In the services industry "Out of sight, out of mind" holds very true.
15. Always protect yourself, the customer and your relationship by agreeing on things up front.  This includes costs, scope of work and handover / success criteria.  Do not negotiate these after the fact.
16. Whenever possible work for and with people you respect. When you do, even the stressful times are easier to deal with.
17. Pre-sales is an art, and the paint brush is 'why.'  Keep asking until you get to the root.
18. Never, ever, bad-mouth another customer or vendor in front of a customer.  Always focus on and sell your strengths.
19. Lastly, no-one who ever bought a drill needed a drill...they needed to make a hole.  I cannot stress enough how important this concept is.