In my opinion, it is in the best interest of any business to keep in contact with their customers every chance they get. I find it hard to imagine why any company would fail to take advantage of free advertising directed to their existing customers.
This contact includes package inserts with brochures, new item announcements, discount coupons for future orders, links to your website, promotional materials like refrigerator magnets with your website address, and if you are lucky enough, paid ads (like the Food Ads mentioned in the question) from companies looking to use your customer base to promote their business.
In addition to package inserts, e-mail marketing to previous and current customers, blog posts, social media and any other possible way you can think of to keep connected with your customers should be used. It will be about the cheapest advertising you could hope for and much more targeted and productive than PPC or SEO paid marketing since you are dealing with actual customers.
Any potential business you can redirect from a selling platform like eBay or Amazon puts more profit in your pocket since you can avoid paying the selling fees these platforms charge.