Disclosure: I have never cross-shopped for any of these services. I use Google Flights, Google Maps for hotel search, and book on the hotel website.
What percentage of the total value is typically saved by those who check different devices, browsers, etc?
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Then you my friend have been overpaying for flights and hotels. Next time you want a holiday, try the classic techniques - Incognito windows, multiple sites, and then compare it with your Google Flights searching
One datapoint me: I never see any difference in flight prices, but I haven't tried VPN-ing into the site from another country. For hotels, prices I find through aggregators can be as much as 50% lower than the hotel's own website price, even when their website claims it's showing me the lowest price.