I cannot promise results from any of these methods, as what you earn will greatly depend on the amount of time, effort, and skill you are willing or capable of putting into them!
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Vending can be a good (if often frustrating) way of making money. Here are just a few tips that can help you vend better. For more detailed guides and information, I'd recommend joining a guild such as t3h vending guild
->Use the Just Added option. go to the mp-> click all listings -> select just added from drop-down box-> just keep hitting the GO button every 10 seconds or so to refresh or hit refresh (hitting refresh actually takes longer)
->the vend refreshes about every 10 seconds, so you can count it to yourself if that helps to know when to refresh ^_^ the closer you can to the top item being at 59seconds or 00 seconds, the better.
When Buying:
make sure is either
-> less than 1/2 price that it says for store price
-> more than .02% less than all the others of it if there is no store sellback price. i normally only go for it if it's less than 1k from all others, and more than 1k difference the more expensive it gets
->buying stuff that can be sold back to stores is normally safer, since you always can sell back to the store for a fixed rate.
->When buying things from rigs, remember that prices will often drop on the bigger items in the second and third rig AFTER the item first appears, so sometimes waiting can nab you better prices.
When Selling:
->try to sell it so it's the lowest in the mp at the time
->don't get into undercutting wars, if nothing else just pull it off the mp and wait (unless it's something you must have sold right away)
->some things are good to buy low and hold onto. like if you get a low price on a rig before it leaves stores, hold onto it for a while and the price will go up