The instinct is to write it protectively, and that instinct costs more than it saves. A restrictive policy reduces the number of people willing to buy at all, and the savings on the small number who would have claimed rarely covers the sales that did not happen. The businesses with the most generous policies in most categories are not being naive.
State the window, the condition, and the mechanism. How long somebody has, what state the thing needs to be in or what stage the work has reached, and what they actually do to request it. Those three answer the entire question, and a policy missing any of them produces the enquiry it was meant to prevent.
Write it in the words a customer would use rather than in borrowed legal phrasing, since a policy nobody can understand does not reassure anybody. If it takes a second reading to establish whether somebody qualifies, it is doing the opposite of its job.
For services, define the stages rather than offering a blanket position, because a service partly delivered cannot be returned. Full refund before work begins, a defined position once a stage is complete, and nothing after final delivery is a structure customers understand. Vagueness here is where disputes originate.
Understand that consumer law may override what you write, which is worth knowing before assuming a clause protects you. Faulty goods, services not as described, and certain distance selling situations carry statutory rights that a policy cannot remove, and a document attempting to do so is both unenforceable and damaging to read.
Honour it without friction when somebody claims, which is the part that determines what the policy is actually worth. A refund paid grudgingly after a process produces a worse impression than never offering one, and the person claiming will describe the experience to others. Treating it as a marketing cost rather than a loss is the accurate framing.
Place it where the decision happens rather than only in your terms. On the pricing page, in the proposal, and near the point of purchase. A policy that only exists in a document nobody opens before buying has no effect on whether they buy, which was most of the reason to have a good one.
Track what actually gets claimed, since the rate is almost always lower than the anxiety suggests. Businesses that measure it typically find the cost is a small fraction of revenue, and that figure is what justifies keeping the policy generous when the instinct is to tighten it after a single bad experience.
Then review it when what you sell changes, since a policy written for one offering rarely describes another. Adding a subscription, a physical product, or anything with a delivery obligation changes what needs covering.
Make it easy to request, since a customer who cannot find how to claim goes to their bank instead, and a chargeback costs considerably more than the refund would have.
State it in your own words rather than copying a competitor's, since a policy describing terms you have not thought through is one you will find yourself unable or unwilling to honour.
Handle the request in one step rather than several, since a refund requiring a form, a reason, and an approval produces resentment out of proportion to the amount and the person describes that process to others.