I recently searched for flights via Google Flights (for Frontier). The price shown for the exact same itinerary was ~$50 more on Google Flights than when I used my smartphone on a different network (disabled WiFi), going directly on Frontier's website. This could be because Google counted for things like, for example, 1 checked bag when comparing all flights.

I don't have enough knowledge on the matter, but I will absolutely use a different device and book directly on the airline's site to ensure I get the best price with no middleman fees.