Apparently, it's not okay to refuse to sell anything to any sane, well behaved, mentally competent, sober, law abiding person in your store who is not violating any posted store rules (dress code, etc.) because it is defined as a business open to the public. Gun shows and flea markets count, too, since the independent vendors - whether owning a business license or not - are selling within the structure of a licensed business open to the public. If you sell in your home or at your yard sale on your private property, you could refuse a purchaser, but would be wide open to civil litigation if they can prove it was discrimination based on 14th Amendment rights; age, gender, race, religion or personal philosophy. That last bit pretty much covers political philosophy, too, unless you are provably or obviously an individual,, or a member of an organization, on the federal lists for terrorism and/or hate crimes.