when i post the product, should i write the big keyword or small keyword to describe my product? for example, if i produce one metal ball . if i wrote balls, someone who need the balls may search my website, but maybe may balls is not he wanted. maybe he need the plastic ball. So even though can bring more traffic but it is uselss. If i wrote metal ball, the traffice will be less, but once they searched the metal ball, they mostly want to buy metal ball. So what is your idea about the keywords? Could i get your advice? I should write big or small( exact to describe my product) keywords? Thanks.