My question is a hypothetical one. Inasmuch as I intend to sell a pinball machine, under contract, to a buyer whom has been fully disclosed the terms of the sale: I wonder if there is there any statute or precedent, particularly in the Uniform Commercial Code, or in my state (California) that would prohibit or void the enforceability of a clause stipulating that after two years have elapsed, I retain the right, during a 30-day period, to repurchase the machine at a 20% premium to the original sale price?