This works with many items that are moderately low cost and have a certain demand, that may be limited. For example, if you need to buy 10 Fruit Blast cocktails for a quest, most likely you don't mind buying them for 10k more. Grapes are one item I haven't heard of so thanks for the update. Some items that are common are:
- Cooking ingredients, chocolate bars at times, some other items you can find especially in the culinary chest.
- Construction items such as: Gold leafs, Marble bricks, etc. (expensive stuff with low supply)
- the BEST one is Clue Scroll required items. Ive researched some popular items needed for clue scrolls, and you have no idea how much money you can make with them. In the past I would buy 500-1k mithril helms (not full) for 350-400 gp each, and sell them for 5k (4995-4999). Depending on if anyone else is currently doing this, you can make a load of money. One time i bought 1k of them for 375k total before a vacation, then i put them in for 4999 each and got 4999k for it. (basically made 4624k) At the time that was huge profit for me, on a mass scale using different items this can be very profitable. WARNING - Idk the market for these items atm, i havent merched them in over a month. (9/27/12 is today). Make sure you try flipping these items before you attempt this method. (find the selling / buying price, then use the margin). If you don't know what that means, look up a simple flipping guide. If they take wayy to long to flip, or have a margin that isnt significant then don't bother.
Goodluck guys, im happy you brought this up.