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Watchwork Sprockets have gone up over 2x what they were worth during the Lion's Arch events. Now is definitely the time to cash in on them as well as Pristine Toxic Spore Samples. Silk scraps do not appear to be going beyond 2 silver any time soon, so I would sell those as well if you haven't already.
Selling isn't the only thing we do here to make gold, so let's talk a bit about when to buy some items that will soon be hot sellers. I predict that Copper ore, Mithril ore, Silver ore, and Platinum ore will all increase after the April 15th patch. The Copper Ore in particular appears to have stopped dropping now that people no longer need blades crafted. You might want to begin buying each of these ores in small amounts leading up to the patch day.
Certain Unidentified Dyes (think red, yellow, etc) have increased in value since it was announced that many changes were coming to color our clothes in Guild Wars 2. While the ship has probably sailed for buying these, I believe that the items used to craft these unidentified dyes will continue to increase. The much neglected walnut (used to be 8 copper on a good day) is now worth 35 copper! This just goes to show why you should have at least one stack of every crafting/food item worth vendor value in the game. You never know when a change will turn garbage into gold, and you don't want to leave it to chance whether you will be fast enough to take advantage of new deals.
Speaking of Unidentified Dyes, they are at 39 silver buy out and 36 silver bid. That is actually almost a profitable scenario for flipping. While they are sure to rise above 40 silver after the patch, do not waste your money buying now. Instead, buy right after the patch when a massive (but temporary) increase in supply drives the prices down to a few silver. Afterwards they will steadily rise, making unidentified dyes a great way to invest your gold long term.
Fine, Masterwork and Rare Dyes are fantastic flips right now! I am making a killing right now flipping for 20%-40% profit each time. Spread out your buy orders and enjoy the rewards.
If you have any dyes from before these changes took place, combine them at the mystic forge and go for some massive profits!
Last but not least, I want to mention sigils. I have tons of them stored in my bank and character bags because I just know that the double sigil change to two handers will make prices soar. I'm keeping all the different qualities just in case it's better to mystic forge instead of just flip.
Keep paying attention to the various updates that ArenaNet is giving us in preparation for April 15th. Oh... and do your taxes if you live in the US.