My track record of getting paid the best price guarantee is pretty poor. Partly through my own fault (for not knowing all the fine prints) but also because there are so many exceptions.
It’s quite deceitful as they give people the thought that they can book confidently knowing the best price is guaranteed, when there are in fact a lot of exclusions (some of which are unfair IMO).

• One time I used 1,000 avios to reduce the price by £10 —> Disqualified me (unfortunately despite a big price difference)
• the next time I had used an e-voucher (which was given to me as compensation for something) to reduce the cost by £100. —> This disqualified me (great, I saved £100 from the voucher, and probably paid the fare £80 more, so only £20 net saving!)
• The third time I was super careful to not use avios nor vouchers. The price difference was big, a few hundred £s. The screenshot clearly showed the (cheaper) fare and taxes. It also added a small fee for the platform, and then a £1.50 fee discount for that platform’s fee. —> My claim was denied because « the flight is discounted »