There are words that show empathy for the other person, but without putting yourself at risk of accepting liability. They can sound a bit mechanical sometimes, and reading from a script isn't much good.
Just letting someone know that you understand that they're stressed and annoyed or frustrated, and that you'll try to help them makes a big difference. At least, it does when people do it with me.
To me, there are few things more infuriating than a Comcast representative saying something like, "Oh, I'm very sorry to hear that. I would also be frustrated if my cable modem were not acquiring a signal." This type of "empathy" has disillusioned me from most empathy used in customer support.
Yes, this is what I mean. Exercise empathy first - even just "I'm sorry, this is obviously frustrating" is a much better start than an angry defense of why you obviously can't include X and Y in the free version.
Just letting someone know that you understand that they're stressed and annoyed or frustrated, and that you'll try to help them makes a big difference. At least, it does when people do it with me.