High quality Mesh items with full perm rights and strong LODs. I don't have an in-world store and therefore only sell at the marketplace.

When using the items they must be part of your own build. Selling the items as they are is not allowed. Linking a prim to it is not considered as 'own build'. There must be clear difference to the original item.

Make sure the rights in your build are set to anything but copy/transfer.

Use in your own creations.
Don't sell them as stand-alone.
They must be completely different than the original item.
Set the permissions to anything but full or copy/modify.