I have worked for large and small companies. In the finance world they all wear ties and look at what it has made of the world economy. At my last job I worked directly with one of the top 200 richest men in Australia. Unless he was meeting with the CEO of another company he never wore a tie.
I think you should dress smart and professionally. You don’t need a tie to close a sale or to make a good impression. You need to look professional and do what sales people do – sell.
I would get over it and just enforce the fact that he dresses smartly.
I like the point about discrimination. Why can females wear t-shirts and singlets on casual Fridays and men have to wear collars. Not fair I say.