Let's clear something up right off the bat: in Windrose, you cannot sell most of your items. There is no use holding on to your outdated tools, weapons, and armor in hope of trading them for a bit of cash; the best course of action for these items is to salvage them at the Disassembly Bench.
The vendors in Windrose are extremely picky and are only interested in specific items.These items are mostly looted from enemies, ships, and Points of Interest. Some of these items will make it obvious where you can sell them, displaying it in their tooltip, but others are a little less clear.
There are 4 different factions you can sell to in Windrose. Each faction has their own desires and will only buy certain items. Whereas these faction's representatives and vendors are located in Tortuga, the Buyers (people you can sell to) are located on each faction hub - an island that the faction calls home.
Here's a list of all the items you can sell and who you can sell them to.
