Don't Say That. Say This.

"No Problem"

If you work in customer service of any sort, from a sandwich shop to the highest level of elite product or service, you should never say "no problem" or "not a problem" when a customer thanks you.

Saying "no problem" sort of carries an implied "...this time." doesn't it?  As if you might have inconvenienced the person providing you with service, but fortunately for you in this instance, you did not. You want to delight your customers, not leave them with an uneasy feeling that they narrowly avoided offending you.

"My pleasure" (a la Chik-fil-A), "Glad I could help", or a simple "You're welcome!" are definitely more positive ways to respond.

"To Be Perfectly Honest..."

Another good one: "To be perfectly honest" or "In all honesty" or any variation of this.  What exactly is implied when someone says this? That they ordinarily are not completely honest, but in this case have decided to forego lying in favor of full candor and truthfulness?  Not likely what is intended, but what is conveyed nonetheless.

"I would suggest...", "I would recommend..."

Remove would from these phrases and they have real impact.  Leave it in and you are making a much more timid and tentative statement.  People want to know what you really think. If you are willing to make a suggestion or recommendation say it with conviction - don't diminish the value of your opinion by making it sound conditional. Unless of course it really is.