For sales situations I'd add these three key questions:
1. How did you come to have what you have now?
2. What do you like about what you have now?
3. What would you like to change about what you have now?
If someone is wanting to make a change the answers to those three questions will let you know how to approach your proposed solution in most cases (if you listen carefully enough). And of course you should always ask, "Do you have budget for this?" no matter what the situation.