Reselling ETS

While some say that reselling is a fairly difficult skill to learn, that's just because they don't want you learning how to do it too. Learn about ETS items, such as paint brushes, certain transmogrification potions, and common battledome items. These can usually be sold for a certain price range that varies naturally by a certain amount. Look around for different transactions, keep track of how much you buy them for, and sell for a bit higher. Try not to rip people off though, just take advantage of the natural fluctuations in prices.

Examples of ETS items include: Faerie Paint Brush, Honey Potion, Sword of Skardsen, Ghostkerbomb, H4000 Helmet

Note: Don't just judge prices by Trading Post prices. While sometimes they may be accurate, more times than not, they are inflated. Sometimes, people will even post lower than normal prices just to trick you into thinking an item is worth less than it actually is. Moral? Don't trust TP prices, but use them as a ROUGH estimate. Generally for ETS items TP prices are a *little* closer to what an item is actually worth.

Wiz Sniping

This type of making money is fairly time consuming, and somewhat variable as well. It involves looking for items that are way below wiz price, usually put there by people that are new to the site. Basically, you go to the Shop Wizard and search for items like Lab Maps, Nerkmids, Paint brushes, or Transmogrification Potions. These things are given out as random events, so it's very likely that someone will put them in their shops for low prices without checking out how much they're worth first.

You can also try sniping codestones or faeries, but these are generally really low in price to begin with, so the profits aren't nearly as high.

Restocking

Some people also say that restocking is a highly advanced skill that not everyone can do. However, this is also not true. While certain shops are both difficult to pick out good items AND difficult to compete in, (such as stamps), every shop can be profitable, especially the ones that stock large amounts of items at the same time. After each restock, take note of which items sell for higher on the shop wizard, then go for those items next time.

Shops such as the Pharmacy or Books are particularly good for beginners. Pharmacy only has a couple items that are good, but stock in mass quantities. Books stocks a LOT of items, and while some may not be as profitable as others, no book will make you lose money, unless you decide to overhaggle tremendously on it. Note that right now, the time when stocks restock are completely random, so if a shop seems empty, just keep refreshing until some new items appear. If new items do not appear for a LONG time, then check at the Tiki Tack shop. If that's empty, you're probably RS banned, which typically lasts about 24 hours.

Sorry buddy, if I'm out of stock, you're out of luck!

Tips/Tricks

When you see an item that's priced for say...2511, don't haggle 2511, instead haggle something easier, like 2555 or 2342 (three numbers in a row and back) Practice haggling numbers on notepad, or even better, play the haggle game on AIM. Have your friend type a number, and pretend you're haggling that number. For example:
Friend1: 125,411.
GoodRSer4: 123123.
Friend1: 6,421
GoodRSer4: 6786