from me only? I rent/lease marina space for customers to store or work on their privately owned boats and yachts. Is it illegal for me to demand in rental/lease contract that my customers MUST purchase ALL parts, supplies, tools from MY boating store only. If my rental customers purchase supplies elsewhere then use them on their own boats, then they will be fined a percentage of my profit loss or they will be evicted. Have I made an illegal contract or violated any laws?