You are absolutely correct, the reason why sellers are not in favor of partial refunds is due to a potential abuse of the system by certain buyers. I have rarely offered/agreed to partial. Only if I knew there was a chance that I may have missed something. Also, I check what kind of feedback the buyer left for other sellers and if I saw a pattern of feedback indicating that the buyer had asked and gotten partials before, no partial here. I have gotten a negative feedback for not giving a partial too and I wear it proudly.That's the main problem with partial refunds--dishonest/unrealistic buyers. I actually went in an edited out the part of my original comment which touched on how it gets abused and why some seller's frown upon partials because it eventually became a rant, but yes, you are correct. It's the buyers who fabricate problems or make a huge issue about the most insignificant little thing who ruin the practical function of a partial refund. Some time in 2011, I had a buyer send me a short note that she wanted a 25% partial refund on the item she bought due to "manufacturing defects" but she did not specify what the defects where. When I inquired, she responded: "The tags are worn on the edges and I like to keep the tags as they are part of the purchase." She was talking about the retail tags, not even the garment tags, but the paper retails tags that showed the price, bar code, etc., lol.
It is true that if you are at a store purchasing an item and it has make up stains, missing button, rip, mots of the time you are offered a 10% discount, but ask for it before you purchase it. It is not likely that if you order something online from a department store and discover that it has a flaw, the store will offer you a discount after the fact. They will tell you to take it back for a refund.