Well, you can just release a product with promos and let the sites marketing team do their bit, but nothing stops you from starting a product thread to gain traction or add a promo vid showing the product in action. I have found that extra effort has really helped. People know before hand what is to come and it generates some hype instead of just being drawn to their attention when it is released in the stores. So yes, you do pay these sites to handle marketing for you, but nothing stops you from giving your work more exposure. That does require more effort, but that is strictly up to you if you feel it is worth it or not.

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