I think Pete's got it right. What happened to you is the norm, not the exception. I don't see what good a contract will do you. What are you going to do, sue them? Not very practical. I did consignment of instruments and various woodcraft off and on for over 30 years before the internet came along to save me. Stores have no vested interest of their own $ in your work. You are not the landlord who will kick them out if they don't pay, not the power company who will turn off the power, or the water company, or the wholesaler who will dump their business in a minute, so you are last on the list to be paid. In their defense, the music bizz is not an easy one, so I do understand their situation a bit, but still don't buy it.Here in my part of the U.S. some stores will do 20-30%, will others are 50% +. Either way, it is still hard to get paid. I still remember one of my first experiences. I consigned a uke to a local gallery. When I checked on it, they said it had been sold, sort of! They put it on a 3 month layaway to one of their board members and I'd get paid at the end of 3 months. In those days I was a starving builder. I never gave them anything again. There are the exceptions, and they are usually based on how close your friendship is to the owner and how supportive they are of your work. Like Pete said, better to work on developing a web presence and get people to appreciate and pursue your work. Luckily I don't have to do social media, but it probably is the way to get noticed fast. Websites are easy and cheap to do on your own. Keep them fresh. I change mine at least weekly. Don't have someone else do your site, do it your self. For better or worse, I can change mine on a whim. It's actually fun to see what happens when you try something new on a site. Good luck. Don't get discouraged.