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In Guild Wars 2, there are several points in the game where players can upgrade their gear from fine to masterwork to rare to exotic. These points occur at different levels, and I'll leave the (easy) job of discovering where those points lie up to you.
Let's look at one quick example. Level 15 to 20 accessories go from fine to masterwork in the span of 5 levels. If you pay close attention to vendor prices versus selling price, you will notice that the fine items all sell for a little bit more than their vendor price. In most cases it is the bare minimum 1 copper above. The masterwork items, however, are selling for as much as three times their vendor costs!
OK, one more example so we can destroy some other markets for people (sorry it is all in the name of education!). Level 30 to 35 gloves. This is the point in the game where rare gloves start to appear (level 35). The masterwork gloves (level 30) are worth close to vendor cost. But the rares are worth an astronomical amount more! In some cases over twenty times their vendor value.
In the case of the gloves, there are still some level 30 masterwork gloves that sell for a decent amount. But the contrast in profit between masterwork level 30 to rare level 35 is ridiculous.
Find these upgrade humps in the game and you will have a figurative choke hold on the players willing to spend so much for such a temporary upgrade while leveling.