When to say no to a gig?

I have a consistent problem with this. I say yes to bad gigs often, and often I don’t know I’m getting the shaft until afterwards. As a musician, where do you draw the line? When (if ever, minus the Super Bowl) would you play for exposure alone? How long, for a residency, would you wait until the money starts getting good? Also, tips on putting your foot down in a nice way if something isn’t working out but you want to preserve the relationship? A restaurant manager that I know and am friends with would like me to play background music for an hour a week for tips and food/bev for 2 weeks, after that it’s a cut of bar sales. In bands I’ve done a million of those but for solo violin, never. He asked me what my draw was and I told him nothing since everyone who has ever hired me to play solo violin had an event they were hiring string music for and the “crowd” was literally the entire reason I was there. So that’s a turnoff, but he also insists he can and will promote me like crazy once I do a couple weeks, which I believe in the sense that he is a professional restauranteur, but he’s not a musician and doesn’t get the difference between people coming to see a band and background music. I committed to one hour of music tomorrow and will honor that but tips plus food has never once been how I’ve gotten paid for a gig like this. Thoughts? Also, I should mention that this is a solo violin gig. I also play in a band, and my band plays these types of gigs a lot but we are used to not making much between us. Also I’m a waitress by trade, am I in a position to turn down free food to basically play easy shit for an hour, when I don’t have to pay anyone else to play with me?