You have more protection than companies like you to think. Knowing the basics turns "sorry, that's our policy" into a conversation you can win. (Specifics vary by country and state — this is the general landscape.)
Broadly, products are expected to be as described, fit for their purpose, and of acceptable quality. When they're not, you generally have a right to a remedy — a refund, replacement, or repair — regardless of a "no refunds" sign.
If you were sold something based on false or misleading claims, that's a stronger position than mere buyer's remorse. Save the ad, listing, or promise that turned out to be untrue.
Hidden fees, bait-and-switch, and deceptive terms are often restricted by consumer-protection law. You can report these to regulators (how to report a business).
Paying by card adds a layer of protection via disputes/chargebacks that cash and irreversible methods don't offer.
A store policy can be more generous than the law, but it can't take away rights the law gives you. When a company hides behind policy, knowing this is your leverage. Check the specific rules where you live for the details.