Trophies are not achievements.
On some quests, parties have a chance to get a trophy. When they defeat the Orc Lord, they have a chance to take his armour, etc. You will see it in the quest log.
When they come back to town, they will offer their trophy for sale. The trophy market is a reverse auction market - every turn, prices will drop and whoever comes first, gets it. So you can wait and get a lower price, at the risk of someone else picking it up before you.
There is also a reserve price. If the auction drops below this price, the party will take the trophy back, not sell it, and offer it again at a later date, or maybe in a different town (once we have multiple towns). The starting price will again be high.
Trophies have one effect: They add reputation.
Right now the actual amount they add is very small compared to what shops have in reputation (or very soon will have), which is another balancing issue and I've done very little balancing so far, so rest assured, when done it will be worth the gold. (among other things because it will be the ONLY way to buy reputation with gold.)
