I understand why you were evasive but depending on the nature of the problem and the circumstances of the listing, i.e., how described, how pictured, etc., answers would vary.
How I would handle it might differ from how others would do it. I generally don't like issuing partials because they're requested too often as a way for buyers to get the item at a price lower than what they'd agreed to. I try to accurately describe and photograph anything that could be an issue and if the listing showed the problem, my stock response would be "return for refund."
OTOH, if I made an honest mistake and missed something, I'd be willing to work with the buyer on an appropriate partial refund to compensate for a possible loss of value resulting from the misdescribed item.
If I suspect the buyer is a PFF (laughingly described as a "professional partial fisher" in another discussion and/or if I believe that the price was commensurate with condition, the "return for refund" mantra would be repeated.
Without seeing the listing, description and pictures, I can't say how I'd handle your specific case. You say you initiated a return. So are you implying that the seller preferred giving you a partial? If that's the case, it doesn't sound unreasonable if it's the seller who's making the partial offer.