In GURPS Dungeon Fantasy, armor isn't cheap. That's true with the armor from Basic Set and especially true for the advanced armor options available in a historical game using Low-Tech or the unusual armors in Dungeon Fantasy 1.
Swords aren't cheap, either. A two handed sword can run you $900, out of starting wealth of $1000, while an axe is a mere $40-50. A knife is worth as much as an axe. Blades are valuable.
So like folks in a lot of video games, my players have found that formerly occupied armor and used swords are great loot when fighting goblinoid foes. I'm fine with this, but I remember spending way too much time in Betrayal at Krondor stashing enemy armor in chests so I could come back, repair it, and sell it. I don't want to run that kind of game, nor have PCs stocking up on wheelbarrows and wagons and NPC laborers to carry empty armor back to town to sell. It's fine that they loot it but not derail the game maximizing it. So I do this:
Old/Combat Used Armor: [100% - (1d6 x 10%)] x Base Value
Since Average wealth characters only get 40% of list . . . this means a steel corselet ($1300) with 20% battle damage (1300 - 20% = 1040) sells for around 416 (1040 x 40%). That's a good deal, but pound for pound it's not great. (Depending on the roll, it'll be worth between 1170 and 520, and sell for between 468 and 208 for those same characters.)
Old/Combat Used Weapons: [100% - (1d6-3 x 10%) x Base Value), minimum 0% (so half the time it goes for full value).
That greatsword? List 900, used it's between 560 (badly used) and 900 (like new), and sells for between 224 and 360 to Average wealth characters.
That's just if I don't already have a value in mind - a rusted out sword is valueless except maybe as scrap (say 5%, if that?), armor with 50 holes in it might be equally useless.
Makes for an easy ruling, I don't need to track anything, and armor/weapons are valuable loot but not so much that you want to stop the expedition and head home the second you whack an orc leader.