I have a friend who is an excellent detailer. His business wasn't large and he provided a very personal level of service. He had some colorful shirts made up with his business name and logo on them. I don't remember word for word how he said it but something along the lines of: (I provide the highest quality automotive detailing anywhere and my prices are affordable. My work is guaranteed. Ask me about it.) Surprisingly he had many people stop to talk to him. He wore these shirts everywhere, car shows, shopping, normal daily activities, once to a gun show that I attended with him. I saw several stop and ask him about his business. He always left them with a business card and got a good number of customers from his effort. I don't think you would get in much trouble doing these even in a mall.