When the customer has price concerns
Don't dismiss the buyer when they push back. I often hear this comment: "If they push back on price, we don't want them! Pushing back on price is an indicator that a client will be high maintenance or worse down the road."
Source: Sales/marketing consultant Mike Schultz
That might not be the case. Buyers are often taught to challenge price in multiple ways. Just because they challenge you doesn't mean they are bad people or are destined to be bad clients. It also doesn't mean they're challenging your value personally.
It often means they're trying to figure out how to engage you and your solutions. Some providers discount; others don't. They're just asking. Hold your ground and treat them reasonably in the process, and oftentimes they'll just come around.