Changing your mind and being sold something faulty are different arguments

The counter hears one complaint and the law hears two

A customer standing at a returns desk usually says the same sentence whatever has happened: they want their money back. Underneath that sentence sit two entirely different claims, and which one is being made changes almost everything about how strong it is.

The first is regret. Nothing is wrong with the item, the buyer simply does not want it. The second is that the goods were defective, misdescribed, or unfit for what they were bought for. Legal systems treat those very differently, and a shop that would have to help with the second is often under no obligation at all on the first.

Changing your mind is usually a favour, with two exceptions

For an ordinary purchase made in person, there is commonly no general right to return goods because you have gone off them. Shops offer it anyway, because it sells things and because arguing is expensive, but a published returns window is a policy rather than a right. Policies can carry conditions — tags attached, packaging intact, a time limit, a credit note instead of cash — and those conditions are generally enforceable because you accepted them when you bought.

There are two important exceptions, and both vary in scope. Many jurisdictions give buyers a cooling-off right for purchases made at a distance or away from business premises, on the reasoning that you could not inspect the goods or were caught off guard. Many also carve out categories where that right does not apply, such as perishable goods, personalised items, or sealed products opened after delivery. Whether any of that exists where you are, and what it covers, is genuinely local.

A fault is a different conversation entirely

Where the goods are actually defective, the buyer is usually not asking for a favour. The seller promised, expressly or by implication, goods of a certain description and quality, and the promise was not kept. Most systems provide remedies for that, and they are typically not something a shop notice can remove for a consumer.

What the remedies are, and in what order, differs. Repair first, then replacement, then a price reduction or refund is a common shape, on the logic that the seller should get a chance to put things right before the sale is unwound. Some systems allow a short early window in which the buyer may simply reject the goods. Others tie everything to whether the breach was serious. Because the sequence decides what you can insist on, it is worth knowing the local version rather than the version you saw quoted somewhere.

Why a sign on the wall settles less than it looks like it does

Notices announcing that no refunds are given, or that goods are sold as seen, are common and are frequently misunderstood by both sides. In many jurisdictions such a notice cannot displace consumer rights that arise from the sale, and displaying it may itself be a regulatory problem. In the same jurisdictions the notice is perfectly effective against a change of mind, because there was no right there to displace.

Second-hand and private sales are the genuine complication. A sale between two individuals is often governed by a lighter set of implied promises than a sale by a business, on the reasoning that a private seller is not a trader and cannot be held to a trader’s standard. That does not mean anything goes, and misdescription tends to remain actionable, but the protections are usually thinner.

Timing decides more of these than fairness does

Two clocks matter, and people watch neither. The first is any short window attached to a specific right, such as a cooling-off period or an early rejection right, which can be counted in days and can be lost simply by thinking it over. The second is the general limitation period for bringing a claim, which is longer but still finite.

Once either has run, the merits stop being the point. That is worth repeating, because it is the most common way an entirely reasonable complaint becomes worthless: not because it was wrong, but because it was raised late. If a purchase has gone badly and the amount is significant, find out what clock is running before you begin negotiating.

The honest limits of an article like this one

Everything above is a description of shapes that recur across many legal systems, not a statement of the rules anywhere in particular. Consumer law is one of the most locally variable areas there is, it is amended often, and the differences are not marginal. A remedy that is automatic in one country is discretionary in the next.

For a small item, persistence and a written complaint will settle almost everything, and that is the proportionate response. For anything expensive, or where a faulty product has caused other damage, a qualified lawyer where you live is the right route. This site is not one, and cannot be.