How I assume customers think:
Yes, we know we've asked you to implement technology A in this project. Yes, we know you've spent X days preparing for this. Yes, we know today is the first day of implementation.. but we find it all too obvious that we use technology B for this project anyway.. just because we can. No, we don't expect you to take any more time to redo some of your preparations. It's all the same anyway, isn't it??
