If you publish your book through a third party, you will be paid net sales. If you have reached a point that you are earning gross sales, you are reading this book for curiosity or fun.
Gross Sales
Gross sales are the actual sum of all sales without any deductions.
Net Sales
Net sales are gross sales minus expenses. Always find out what deductions all third parties, such as publishing houses and agents, require from each sale. If the gross profit per each book sale is $3.00, find out the cost of all expenses so you will know your net profit.
There were months in which I earned more income from my social media accounts than from book sales. I receive gross profits from my social media accounts because I only have to pay taxes. There are no deductions from the profits I receive from my social media accounts such as print, hosting, or employee costs. I receive net profits from my book sales because I pay print and various third party expenses.