The author is responsible for all copyright use or potential copyright violations in his or her files. For you to make use of another person’s work you need an express license to do so. So for example if you purchase a stock audio file you are not buying the audio file, you are actually purchasing the license to use that audio file in a certain way.
Different licenses allow you to do different things. You need to look carefully at licenses to see what they permit and what they do not. Specifically to use an asset like a template, music loop or preset in an item you want to sell on the ProducerBox Marketplace, you need a license that allows the asset’s use in items for resale and redistribution.
In plain English, the license has to say that you can use it in something you’re selling and distributing. If you don’t have such a license you may be unlawfully profiting from another person’s work!