This is an easily debunked myth, for first-party direct bookings. Third party aggregators and package deals are shady as hell and do all kinds of tricks. But I challenge you to record a screen cast proving that you're seeing different prices for a direct booking for the same ticket (including fare class) just based on different browsers or profiles.

I have done that at least a few times in the last few years and I've never found anything cheaper than Google flights then booking directly with the airline.

Bonus points I'm not booking through shady websites like Expedia.