Your recourse is to sue the customer (the contractor) for the money they owe you: you would sue for breach of contract (violating the agreement, even if only on unwritten one, to pay for the sod) and for "unjust enrichment"--but being unfairly and inappropriately benefited by getting your sod without paying for it. After you sue and (presumably) win, you can then put a lien on the contractor's property, or levy on his bank accounts, to recover money if he still won't pay.