| Morbidsoul |
The merchant's profit is already accounted for in the fact that the item's book cost is normally twice the cost to make the item. A merchant makes a +1 sword for 1,000 gp and sells it at 2,000gp for a 1,000gp profit - or splits the profit with a crafter. Mundane items created using the craft skill have a materials cost of 1/3 book price.
Of course, some of that "profit" might go to non-materials costs like maintaining a shop, or security if the merchant's stock is particularly valuable, so not all of the 1,000gp earned on a +1 sword goes into the merchant's and/or crafter's pocket. But the profit exists somewhere in the 2x to 3x markup between the crafting cost and the book price for the item. The book price is supposed to be the price items are normally sold at.
You do bring up a good point that I never really thought of, but if I were to change it at this point in the campaign it would seem weird. Something to keep in mind for the next one for sure though.
To be honest though, I'm pretty generous with the amount of gold the group receives, so it hasn't been an issue as of yet.