Nearly one in three Americans received a surprise medical bill over the past two years for hospital procedures and healthcare services they believed their insurance policy would cover.

That’s the key finding of a new national survey by Consumer Reports that also found most Americans are so confused about their rights to contest an unexpected health bill that more than half (57 percent) simply pay the bill in full.

“For years we have heard horror stories from consumers hit with surprise medical bills following routine and emergency procedures,” said DeAnn Friedholm, director of the policy and advocacy arm of Consumer Reports.

“Even if you go to a hospital in your network, the unfortunate truth is that there is no guarantee that all your treatment — whether it’s the radiologist, anesthesiologist, or lab work — will be treated as in-network, leaving patients owing thousands of dollars they never anticipated.”

But experts note a handful of negotiating tricks can almost always get you a reduced bill. In fact, a second Consumer Reports survey found that a whopping 93 percent of people who haggled over medical bills were successful in cutting their final costs.

Here are four tried-and-true negotiation strategies:

No. 1: Don’t pay your bill immediately. Paying up right away is a bad idea because it gives you less time to review the charges and makes it harder for you to recoup that money later if you discover errors. A better strategy: Delay payment until after you’ve examined all of the charges on a bill for mistakes and overcharges, which are surprisingly common.

A recent analysis of Medicare claims by the Web-based consumer advocacy group NerdWallet found, for instance, that nearly half contained billing errors. As you leave the hospital, ask for an itemized bill that explains each charge. You may find coding mistakes or charges for services you didn’t receive.

No. 2: Check your health policy. Before paying any medical bill, obtain what’s called an “explanation of benefits” (EOB) from your insurer compare what your policy covers against the medical charges you’re being asked to pay.

If you’re confused about any changes on your bill, ask for an explanation from the hospital, your doctor, or the insurance company.

No. 3: Comparison shop. Healthcare costs can vary by hundreds or even thousands of dollars — even for the same procedure in the same city. A recent study by Blue Cross/Blue Shield found the cost of having a knee or hip replaced can be up to four times more in one medical facility than another — even in the same area.

For instance, a knee replacement averaged $31,000 in 64 markets where BCBS analyzed its claims data. But in Dallas, it ranged from $16,772 to $61,584.86. Across the U.S., replacements costs as little as $11,317 in Montgomery, Ala., and up to $69,654 in New York City.

Knowing the going rate for your particular procedure in your area can help you negotiate down your final bill.

To find such information online, search for the “Current Procedural Terminology” (CPT) code — an American Medical Association code for various procedures. You can also check the Medicare Website for customary charges for certain services.

No. 4: Be professional, but firm. Once you’ve done your homework — and have your documents and price comparisons — in hand, schedule a meeting a medical billing staffer to negotiate your costs.

Experts advise putting your concerns in writing, and you can also try resolving disputes by phone. But a face-to-face meeting is usually the best way to bargain with someone in the business or billing office of the hospital, clinic, or provider that performed the service. Tips for successful negotiation:

• Make sure your anger is under control and you act professionally, in laying out your concerns and demands.
• Negotiate with an attitude of cooperation. Ask: What can WE do to we resolve this issue?
• Provide copies of competitors’ charges and any other documentation that bolsters your argument for a reduced bill.
• If you don’t get any satisfaction with the hospital or healthcare provider, take the issue up with a hospital CEO (via letter), the doctor involved in your care, or your insurer.

If these appeals aren’t successful, contact your state’s health insurance department or attorney general. Every state has a patient advocacy division to help settle billing disputes, but 87 percent of respondents to the NerdWallet survey said they didn’t know how or where to file an appeal in their state.

“Opponents of legislation to strengthen consumer protections against surprise medical bills often say this isn’t a big problem for consumers and point to a lack of complaints at state insurance departments,” said Friedholm. “This survey clearly shows that consumers want to complain about bills, but don’t know who to contact or even if they should be complaining.”