I`ll propose that all of us have two categorical ways to look at all of life and our purpose here. We have to choose one of them. The one is to simply "get through it." In that view, life is a series of reactions and responses to circumstances, fortunate opportunities, wishes and hopes, and accumulation of wealth.
The other is that life is a platform of some kind for a purpose. In this other view, all of history and human culture generally suggests that there is a basic purpose to each life, somewhat like a "destiny." The evolution and development of some type of ongoing aspect of "self" learns and experiences each life, developing in some way.
Following each basic view, all of us develop rules and principles of how to live. Each of use chooses a morality based on our philosophy. That morality can be just about anything, but with thousands of years of history, most moralities have been described and listed.
If you see things the first way, that life is a set of reactions, then your logical solution is to let the transaction stand and deal with possible consequences if or when they arise. If nothing happens, you`re no longer involved. If something happens, you worry about it at that later time.
On the other hand, if you follow the second category, then you have to evaluate both your business and your own personal "quality of self." Speaking to your buyer and indicating a less-than-promised (or optimal) product will impact your business and your cashflow.
One possible outcome is a request for a complete refund. The consequences of that could bankrupt your business, or it could introduce a level of respect for such abstractions as honesty, customer satisfaction, reputation, and so forth. The gamble is whether your buyer values these kinds of abstractions.
An argument toward the refund would be that if your business bankrupts, "at least" you can live with yourself on a character level.
So the bottom line question is this: how important to you, on your own, is this sense of your own character? Which will you choose: practical business, or a risk that your buyer doesn`t assign value to character abstractions.
Saying the same thing in common language we hear every day, you`re the one who has to look in the mirror every morning or evening. Would you rather pay the bills on the basis of a low-quality product, or lose the business (possibly) or struggle with the bills on the basis of your vision of some concept of character.