• Missed a doctor's appointment? You could get hit with a "no-show" fee.
• These fees can be as much as $100.
• Here's what experts say about the fairness of such charges, and how to avoid them.

If you miss a doctor's appointment these days, you could get hit with a "no-show" fee of up to $100 — or more.

This happened to me recently for the first time, and the charge was a steep $150. When I complained to friends and family, I learned that my experience wasn't unusual: Most had dealt with a similar fee.

I talked to experts and consumer advocates about why such fees are becoming common, if the charges are fair to patients and how to best avoid them.

Fees are a 'disincentive' for late cancellations, no-shows

"I very strongly support such fees," said George Loewenstein, an economics and psychology professor at Carnegie Mellon University.

"Patients who don't show up are taking up appointments which other patients could use," saisd Loewenstein, adding that "without such a fee, patients have little if any disincentive for not bothering to cancel appointments well in advance."

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Certified financial planner and physician Carolyn McClanahan said the fees are "totally fair."

"If a patient doesn't show up, that cost the practice money," said McClanahan, a member of CNBC's FA Council. "The doctor and their staff is left with nothing to do and everyone still needs to get paid. Also, that empty slot is a time that another patient can get the care they need."

Penalties shouldn't 'become a profit center'

Caitlin Donovan, a spokesperson for the National Patient Advocate Foundation, said "no-shows" are a reoccurring dilemma for doctors.

But, she said, "to solve this problem is not to charge patients more fees, which many can't afford."

She's heard of medical offices having success with call and texts reminders to patients about their appointments. Patients should always be given the opportunity to bow out, she said.

That doesn't always happen.

Earlier this month, my sister, Janna, tried to call her doctor twice to cancel her appointment for the next day.

"I was in elevator music purgatory for over 20 minutes," she said. Both times, she didn't get through to anyone. Three weeks later, she got a bill for a $100 "no-show" fee.

For my appointment, I did get a call the day before from the doctor's office. But when I told the woman I'd forgotten about the appointment and couldn't make it, she said I'd still be charged a cancellation fee.

Adam Rust, the director of financial services at the Consumer Federation of America, said that using a fee to recover costs may be reasonable.

"But if penalty fees become a profit center, it may incentivize trickery and deception," Rust said.

In addition to sufficient reminders and opportunities to cancel appointments for patients, there can be other creative alternatives to "no-show" fees, Donovan said.

She recently spoke to one medical group in Camden, New Jersey, that had a problem with patients standing them up. They started asking people why they hadn't come. Many said they just didn't have reliable transportation to get there.

"They implemented a ride share, which came at a cost to the office, but their attendance levels went right up and more than compensated for the cost of the rides," Donovan said.

Fees shouldn't hurt credit, still may be worth disputing

When you make a doctor's appointment, ask about the office's policy around late cancellations and missed appointments, Donovan said. If you're told you'll be charged for missing an appointment, ask if you can reschedule it instead.

You can also try asking the office if they can waive the charge if you find it unfair or if you can't afford it, she said. They should work with you.

"Ultimately, these fees are discretionary and I would be reluctant to work with any office that inflexibly charged them," Donovan said.

On a practical note, debt owed to a doctor's or dentist's office is considered medical debt, a spokesperson for the Consumer Financial Protection Bureau told CNBC. Such debts that are less than $500 are not reported to the credit bureaus, they added.

As a result, it seems unlikely that a no-show fee would harm your credit.

When my sister Janna got her no-show invoice, she simply called the number on the bill and explained that she'd tried without success to cancel her appointment. The customer service agent agreed to waive the fee immediately.

"I feel like they have a system where they send out the bill for a no-show and then if people make the effort of calling it to question it, they'll get rid of it," Janna said. "But there are some people who are just going to pay it, so they bank on those people."