Degustacje, degustacje, degustacje! - Deciding Whether Two Items Make a Fair Swap

A friend suggested swapping two of my skins for one of his, and I am finding the comparison harder than a normal purchase. I like his item, but adding together two numbers does not tell me whether I would miss the skins I already use. We both want the exchange to feel fair, and neither of us wants a small disagreement to spoil our usual games. How would you discuss the trade without reducing everything to a single total? I would prefer to reach a clear decision together, even if that decision is to keep our own items.