help

some one took my art pieces, and promised to pay me. I left the art pieces for him and got his two checks, one check returned, once check cashed. From the way he handled my payment, I decide not to sell him my art pieces anymore. I want my art pieces back, but he refused, saying he already gave someone else to sell my art pieces. but he not even fully payment, how can I get my art pieces back? I will return him the partial payment he gave me.