"I didn't know the Vine Cord Sandals were duped, and I spent a lot of money on them! How do I avoid this situation in the future?"

It's a very tough situation. There are thousands of different items in UO - some common, some rare, some truly unique. They come from dozens of different sources - some are looted from monsters, some are received from quests or events, some are stolen from NPCs. There is no easy way to catalogue each of them. Your best bet for information about the lore of a particular item is your fellow players - either in game, or on a forum like Stratics or UO Forums

If you are planning to buy an unusually expensive item, do your homework. Make sure the vendor you're dealing with has a good reputation, and make sure the item you're buying isn't... notorious. Because we are committed to cleaning up dupes, exploits, and cheats, there's no guarantee that an illegitimate item will still be there tomorrow, and owning these items - particularly in large quantities - puts you at risk of account action.