@Zero101 But it's the difference between "luxury" and "necessity". Inns and food can make a more consistent profit, because everyone needs them so they can afford to charge less. However Jewelry is a luxury, so it likely won't sell often meaning they typically cost quite a bit. Normally that neckless would be too expensive for the average commoner to buy on a whim.
However, this is a fictional world so maybe the author didn't deemed this logic worthy of existing there.