To make sure the right ads get to the people most interested in it, Google shows ads based on its users’ search history. A user searching for “coffee” for example may see an ad for a coffee mug on the next page. But can airlines also harness that same personal data to increase the price of a particular flight?

Consumers may wonder whether airlines and ticketing websites raise airfares for consumers who research a specific route on their computer. However, airlines say prices change not because of a consumer’s search history on a website, or their cookies, but because of inventory updates or glitches on the website, FareCompare’s Rick Seaney said in an email.

“If the airlines were to raise prices because of browser cookies (targeted individually) there would be air travel whistleblowers and senators running to microphones for legislation to prevent it,” said Seaney. “What people see when they shop multiple times and prices are changing is a reflection of inventory changes, data caching techniques and the fact that prices generally get more expensive closer to departure date, even within a day.”

Still, William McGee, an aviation adviser for Consumer Reports, says he’s seen evidence that this pricing based on search history may not be entirely a myth.

In a 2016 study, McGee and his team conducted 372 searches on nine airline ticketing websites. The searches were simultaneous with the exact same itinerary and website but two different browsers — one with its cookies intact, another one that was scrubbed.

McGee found that 59% of the times when the searches differed, the fares were higher on the scrubbed browser — the browser with no search history — but those higher fares often came from online travel agencies such as Orbitz. The lower fares on scrubbed browsers tended to come from meta-search sites, such as Google Flights or Kayak.

But McGee couldn’t say for sure why he saw those different results.

“This is a very opaque industry,” he said.

The best thing to do? Just shop around.

“Our takeaway advice is that consumers shop around, and … if its possible, to search on at least two different browsers,” he said. “If you see different results … you clearly want to go with lower ones.”

The Leadership Brief. Conversations with the most influential leaders in business and tech. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Contact us at letters@time.com.