Implied warranties vs. "no returns or refunds" signs

I often see stores (especially small businesses) with signs saying, "ABSOLUTELY NO RETURNS OR REFUNDS" or some variant thereof. However, from what I understand, there are various implied warranties under the UCC which businesses must comply with. How does the UCC interact with "no returns" signs?

If the law states that customers can return defective goods within a warranty period, then no sign in the shop can deny them that right.

The shop owner can use such a "no returns" sign to make it clear that they don't accept any returns that are not legally mandated. For example if you bought something, but at home it turns out the colour doesn't fit with the decor of your house.

In short, the shop owner cannot overrule the law.

australia

The Australian Consumer Law imposes consumer guarantees on the supply of goods and services that exist independently of any contract or supplier warranties. One of these is the right to a refund or replacement if there are major defects.

At the same time, the ACL prohibits deceptive and misleading conduct in trade or commerce, which the courts have held, includes providing misleading or deceptive information about consumer guarantees. Such as a sign saying "ABSOLUTELY NO RETURNS OR REFUNDS" when the consumer has a right to these under law.

The maximum penalty for a corporation is $50 million and $500,000 for an individual. This article lists some of the actual fines that have been imposed for breach of the ACL but not all are related to no refund policies. The biggest fine I know directly related to no refund policies is the $3 million imposed on Valve, the operator of the Steam online gaming store.