Retail pharmacies are now responsible for around 1-in-5 flu shots given to Americans each year, and many of these stores advertise low-cost or no-cost shots for customers on certain health plans. But a survey of Walgreens locations in New York City and Los Angeles finds that nearly half of the flu shot recipients at these stores are getting bad information about whether their insurance policies cover the cost of the shot.

The folks at Change To Win (a group that admittedly has little love for Walgreens management) sent people to 50 different Walgreens in NYC and L.A. to get flu shots using 8 different insurance plans.

According to the report [PDF], in 40% of visits, a Walgreens employee chose to not scan the customer’s insurance card, claiming to be certain whether that insurer covered the shot or not.

And it looks like they should not have been so sure of themselves, as CtW found that 48% of visits resulted in customers receiving inaccurate information from the store employees.

This could mean that customers paid when their insurance would indeed have covered the bill for the flu shot, or that the customer was incorrectly told their insurance covers the cost of the shot, meaning they’ll get hit with an invoice when the claim is rejected.

In some cases, the customers had two cards for their health plan — one for pharmacy purchases and one for medical visits — but in 2/3 of the cases in which the first card was denied, the Walgreens staffer would not check the second card to see if that one worked.

It’s surprising that Walgreens has not cracked down on how in-store flu shots are handled, after being spanked by the New York State Attorney General in 2012 for misleading thousands of state employees into believing their insurance policy covered flu shots at the drugstore chain.

While the CtW report focuses solely on Walgreens, we can’t believe that this sort of bad behavior is only happening at one company. And even if it is, there are things you can do before you get your shot to vaccinate yourself against this ineptitude.

The main thing is to confirm with your insurance company whether your plan covers flu shots. Yes, it probably means waiting on hold to get a real person on the phone, but this information is vital ammunition in the war against getting screwed at the cash register.

This vaccine-finder tool can help you locate retail locations and clinics that offer vaccinations for flu and other ailments in your area.

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.