Scammers causes real and honest businesses damage

I bet everyone around the world have seen a lot of scams on the internet or on social media platforms. For honest and "real" businesses this causes real problems when trying to advertise your business, customers generally think that everyone advertising a business or service on these platforms are scams, but when all you do is trying to do is raise awareness of your business.

I had a customer phone me last week seeking prices on various types of bricks, I then invited him to come and visit me to see what we do, to my surprise he phoned and cancelled his order due to us not having enough stock on the floor when he visited, but when I explained that we had a busy couple of days and that most stock was sold he said that he's afraid I will steel his money and disappear.

How do you convince someone like that that you do business honestly? Any suggestions?