
The third method :
the pinned post of your group, it must be a commodity, but do not put this post from the beginning because in this way you may kill the group and eliminate it completely, meaning that the pinned post must be related to profit, but it is changed with time.
Fourth method : Affiliate and Affiliate is to sell a product that you do not own but owned by someone else, this product you may bring from Amazon oak bank and display it on your group, and it will be in your niche.
And put a description of the product with the link.