I’ve never been in business for myself in the aspect of “owning a business”. However I do detailing on the side for friends, and co workers. Similar to a vast majority of things in life such as a restaurant. If you ask about a restaurant and someone you know who’s been there says “don’t bother, service sucks, and food isn’t worth the money”. I think often times we would pass on that business because it wasn’t recommended. I say owning a business and such of this nature word of mouth can make a break anything. I don’t mean to say that you’re not established, or anything like that. However that’s how I’d look at it. I’d just be polite and tell him with his budget, and requests you don’t feel it’s right for you as a business. End on a high note.