I've seen this at airlines too. I look at a flight, see an ok price, spend 10 minutes checking with my boss for the days off and go back to book it and it's 40€ more.

Last time I saw this I tried it from a colleague's phone and they got the original price. Refreshed both and the difference remained.

This should really be illegal. And I believe it is here in Europe. That other shit that Chinese sites do ("another user just bought one of the last few remaining!!") is illegal here too. In the end I didn't take the flight and booked the next day from home when it was the cheaper price again.