Not to get into a shouting contest with you, but I beg to differ on the Visa policies. You may own a business, but I deal with Visa policies as a job.
What you have described is a Reason Code 85 (Credit not processed, aka Buyer's Remorse), Condition 1.
This is straight from the Visa chargeback policy manual. I have bolded all the important parts, but feel free to read the whole thing.
What Constitutes Proper Disclosure?
Cardholders should be made aware of the merchant’s return policy at the time of purchase. When not properly disclosed, a chargeback is valid when the merchant : does not accept a return/cancellation, does not credit for the full amount, or only issues "in-store" credit. The following guidelines are offered will assist in clarifying what constitutes proper disclosure.
• The merchant’s cancellation/refund policy disclosure must be clear and concise, and must not be open to interpretation.
• Refund policy must be legibly printed in letters approximately .25 inches high near the cardholder signature area. Note: It may also be initialed.
• A mail order merchant must include disclosure of its refund policy on the order form. invoice, or contract.
• An electronic commerce merchant must communicate its refund policy during the order process and require the cardholder to select a "click to Accept” or other affirmative button to acknowledge the policy before completing the transaction. The merchant’s refund policy must not be on a separate screen that the customer has to click to open.
• If the cancellation/refund policy is on the back of a receipt, the cardholder must sign or initial the back of the receipt as evidence of proper disclosure.
• If the refund policy is embedded within the pages of a multi-page contract, the cardholder must initial that particular section of the contract for the policy to be considered properly disclosed.
• It is not proper disclosure when cardholder signs a electronic signature capture pad when the disclosure (i.e. All Sales Final, No Refunds) is not on the pad. Even though the receipt contains the policy the cardholder was not made aware of it prior to signing it.
Verbal Disclosures:
• Verbal or store signs is proper disclosure when the cardholder acknowledges they were informed of the policy at time of purchase.
• If merchant indicates verbal or store signs disclosed policy, your case needs to include the cardholder’s rebuttal indicating disclosure was not provided.
• Proof of merchant disclosure can not be a recorded phone call.
Disclosure Verbiage:
”NO REFUND” - Merchant that does not accept merchandise in return or exchange, or issue a refund to the Cardholder.
”EXCHANGE ONLY” - Merchant that only accepts merchandise in immediate exchange for similar merchandise of a price equal to the original Transaction amount.
”IN-STORE CREDIT ONLY” - Merchant that only accepts merchandise in return and delivers an in-store credit that equals the value of the returned merchandise and must be used at the Merchant’s place of business.
********
As long as the customer says that they were not verbally told that returns were not allowed, or that there were no large signs stating no returns are accepted, the customer would win in a chargeback arbitration. So even if the cashier were to say "you have 30 days to return or exchange blah blah blah", all the customer has to do is say "Nope, they never told me anything". They don't have to prove anything. Nothing. Zip, Zilch, Notta.
Again, I am not looking at getting in a shouting contest with you, I am just listing all the proper Visa policies in case someone has a similar problem in the future.
I wish I knew more about Discover, American Express, or Mastercard regs, but I don't! 
