The only way I have been able to manipulate pricing in my favour is to use AA rather than BA to book.

As an example, booking LAS - LHR - NCL and return with BA uses the US POS and charges me in USD. The same is true if I use aa.com (ignoring for simplicity's sake the fact that I am then booking AA codeshares rather than the BA prime flight number).

However, if I go to https://www.americanairlines.co.uk and look for the same LAS - LHR - NCL itinerary it will quote me in GBP using the UK POS. On some occasions it is cheaper to book in USD and on other occasions it is cheaper to book in GBP. Ditto for booking in EUR via AA's site in Germany.

There's no magic or subterfuge involved. No VPN. No masking my IP address. No deleting cookies. Just using the system as it's designed to be used, only to my advantage.