Regardless of what items you were selling in the game, the prices would always fluctuate based on the market's demands.
For example, the headquarter title deed. During the early stage of the game the price of it was very low, around 500 gold or so, since there weren't many guilds that could use it. The only problem was that the price of gold was extremely high during this period of time.
But now, there were many players that had reached level 20, hence the number of guilds that wanted to establish their own headquarters had been steadily rising. Because this increase in demand and the limited supply, the price of a title deed was currently about 1000 gold.
But because of how rare it was, it was hardly ever seen on sale.
Sanguine Warflag's problem with Fearless' demand wasn't that the price was too high, but that he wanted 500 gold regardless of whether they successfully completed the dungeon or not.