Interesting observation.

Booking.com just tried scamming me into paying 400€ more on a hotel just because I opened the page when signed in with my existing account. Opening the same page from a fresh session and *then* signing in gives me the discount again.

So make sure to search for your hotels without signing in first, I guess... or don't use booking.com - but let's be real, it's not like other sites don't do the exact same thing.

I hate this.

@can out of curiousity, what was the price before that 400€ markup attempt? (Having just spent a few thousand € via Booking-dot-com I'm wondering about the percent increase I might have been fleeced for)
@maphew it was a 10% “genius” discount for me signed in, and a 30% “special” discount signed out. So… I think it was about 1900€ for the entire period with the 10% discount. (was just checking prices with a friend when I noticed it, not actually buying)
@can thank you. I used this example (anonymized and converted to CAD$) as part of my submission to the Canadian competition bureau. Unfortunately there's no way for me to go back in time and see what my logged/logged-out prices were for the places we used Booking.com for on our trip to add weight. Your story does give me a tactic to use for next time though!