I HAVE A STORE, I MADE THE POLICY: NO RETURN, NO REFUND,ONLY DO EXCHANGES FOR ITEMS WITH MANUFACTURER''S DEFECTS. IS THAT LEGAL? IS IT ALL RIGHT?

Within limits, such a policy may possibly be enforceable, although it is not a particularly good customer-service policy. There are certain liabilities that you cannot legally disclaim through such a policy, including your liability for defective products that cause personal injuries.