Most hearing-aid purchases go off without a hitch. But some don’t. It’s not easy to get things right because each patient’s hearing loss is unique, and every patient has different expectations. Even two patients who have the same hearing loss on paper may have very different rehabilitative needs.

Also tricky: Since most hearing aids sold by local hearing specialists are custom-molded, patients can’t feel exactly how various makes and models would fit in their ears. But it is possible to try different technologies. Many BTE models with disposable earpieces can be fitted with special pliable earpieces and then set up for tests. The sound quality in the test should be fairly close to what you’ll get with your own customized device. But ultimately, time and experience with a particular hearing aid are the only ways to determine how well it works for you.

For aids bought from hearing specialists, most offer a trial period during which you have at least 30 days after buying a hearing aid to return the aid for a refund. You may, however, still have to pay a portion of the hearing-aid costs. That portion varies tremendously from company to company: Some charge nothing; others charge a flat fee of $50 to $100; others charge a fee equal to 10 percent of the price of the hearing aid(s). It is important to ask about refund policies and get a dispenser’s policy in writing.

Sellers of OTC models probably will offer less generous return policies.

Some specialists offer trial periods more generous than 30 days. Some allow 60 days or more for wearers who have special needs or who have bought particularly complicated hearing aids. If you feel you might need extra time to decide, ask the dispenser if an extension is possible and get the dispenser’s promise in writing. But keep in mind you’ll likely face a time limit: The FDA considers hearing aids “used” 90 days after they’re sold, and few sellers will take them back at that point.

Hearing-aid specialists usually offer a free adjustment period during which they’ll provide assistance. This period varies, with some sellers offering free adjustments for six months and others for the life of the aid. If you are buying a hearing aid for the first time, or trying a new type of aid, find out about the dispenser’s policy regarding follow-up appointments.

Also, find out whether your return period will be extended if adjustments are necessary; if so, get this promise in writing. You don’t want to lose your right to return an aid simply because you’ve spent weeks trying to get it adjusted to meet your needs before concluding that it just doesn’t suit you.

To back up newly purchased aids, most manufacturers provide warranties of one or two years. In most instances, you can buy an extended warranty too.

You can also buy hearing-aid insurance to cover damage or loss, either as a manufacturer’s warranty add-on or as a separate policy. A hearing-aid dispenser should have insurance information; also check with your homeowners insurance carrier—you may be able to add a personal articles floater for hearing aids to your policy. Before buying any insurance, compare its premiums to the price of the aid. Usually, it’s not a good value.

With luck and effort, you won’t need to buy new hearing aids that often—the average lifespan of new models is five years. By keeping yours clean and maintained, it will likely last longer.