"No problem" is not an appropriate answer to "Thank you" -- especially in a business setting. The appropriate answer to "Thank you" is "You're welcome," "You're very welcome," or "It was my pleasure." If you are functioning on behalf of a business, it is a given that customer service is not a problem. If it is a problem, you need to get out of that business.
As a customer, anything I ask for short of a pint of blood is "no problem." You are in customer service -- no matter what your title is, if you interact with people, you are in customer service. No matter your business, your customers are -- or at least should be -- your main concern. With all the online services to rate businesses of all kinds, you can't afford even one disgruntled customer with a computer.
I've heard that a happy customer tells four people and than an uphappy customer tells twelve. And that was before computers. Now an unhappy customer can tell thousands -- from your office, waiting room or store! Happy customers are less likely to take the time to the time to write something positive about your business. You don't get extra credit for doing the basics.
I've taken to saying "I would think not" when someone says "No problem" in reponse to my "Thank you." And as unfortunate as it is, not one person has understood what I was talking about. Most of them cocked their heads at me like a confused puppy. I can just envision the conversation bubble over their head saying "Huh?!?"
I guess I'm just becoming a grumpy old lady but I think our language should be managed better -- and that customers should be treated with more respect.