California refund policy: does every store have to accept returns?

No. California generally allows retailers to set their own refund policy, but a store that will not provide a full refund, credit or equal exchange within seven days must clearly display that limited or no-refund policy before purchase. If it fails to display the policy as required, California law can allow a return with proof of purchase within 30 days. Official source: California Attorney General Refund Policies. Guide: https://getinstantlaw.com/us/california/consumer-rights