Kosher certification organizations charge manufacturers a fee for kosher certification. This fee covers the expenses of researching the ingredients in the product and inspecting the facilities used to manufacture the product. There are some who have complained that these certification costs increase the cost of the products to non-Jewish, non-kosher consumers; however, the actual cost of such certification is so small relative to the overall cost of production that most manufacturers cannot even calculate it. The cost is more than justified by the increase in sales it produces: although observant Jews are only a small fragment of the marketplace, kosher certification is also a useful (though not complete) point of reference for many Muslims, Seventh Day Adventists and vegetarians. In addition, many people prefer kosher products because they believe them to be cleaner, healthier or better than non-kosher products. It is worth noting that kosher certifiers are not the only organizations that charge for the privilege of displaying their on a product: some charitable organizations allow manufacturers to display their logo in exchange for a donation, but unlike kosher certifiers, those charities do not perform any service in exchange for that payment.