I wouldn't follow NPC prices as the 'real' prices of the Eorzean economy, because those prices are thought to balance the in-game economy, not for lore accuracy.
Using K'nahli's method (being vague or letting it be on the air) seems the most rational choice, to me. Since the game has no actual lore about the value of gil (remember: prices are balanced towards gameplay), it would be very easy to run into people claiming that your prices are really cheap/expensive because they don't line up with their particular microcanon economy.
Using K'nahli's method (being vague or letting it be on the air) seems the most rational choice, to me. Since the game has no actual lore about the value of gil (remember: prices are balanced towards gameplay), it would be very easy to run into people claiming that your prices are really cheap/expensive because they don't line up with their particular microcanon economy.