Since launching the Blender Market a few years ago we have seen a wide range of products submitted. Some are great! Others not so much. This is to be expected, but in most cases there's a clear distinction between those products that pass inspection and those that don't.
The products that pass inspection and go on to do well, selling many copies, do one thing: solve a real problem.
If you're building products for the market, or considering it, then try this exercise: look at the top-selling products on the Blender Market and ask yourself, what problem is this product solving?
The top three products, by sales, at the time of this writing are RetopoFlow, BakeTool, and Gaffer. Let's explore the problem they're each trying to solve and how.
RetopoFlow - view
Problem: retopology is incredibly tedious, requires many steps to setup, and it's not fun for the vast majority of people.
Solution: make retopology more like sculpting by enabling artists to draw on their high-res object in a single step.
BakeTool - view
Problem: baking requires many steps to get started and then requires repeating those same steps for every single object and every single pass
Solution: turn baking into a jobs system, whereby each job can have it's own settings and objects, enabling artists to bake dozens of objects and passes in a single button-press.
Gaffer - view
Problem: managing all the lights in your scene, much less cycling through your HDRI library to find the perfect one, is very cumbersome.
Solution: bring all lights into a single panel, adding viewport highlighting for quick and easy management without ever changing context.
Notice a pattern? Each of these products expedite, in some way, a portion of the artists workflow, enabling the artist to spend more time and energy on the things that matter; creating results.
All three of these products make a concerted effort to solve a real problem that artists face every day. That's the key to their success.
If you're a Creator that's looking to build a product for the Blender Market or for anywhere else, then ask yourself this:
What problem am I solving?
If you don't have an immediate answer to this then you may need to revisit your idea. If in doubt, solve your own problem. Identify a slow point in your workflow, ideally something you do often, and find a way to automate or otherwise improve it. As they say, time is money.