I want to start of by saying that this isn't guaranteed to work every time. What you can do is buy uncut gems from Gem Traders, and then Server Hop to buy them out again. The Al Kharid gem trader stocks 1 Uncut Sapphire and 1 Uncut Emerald. The Falador gem shop stocks 1 Sapphire. Sapphires buy for 25gp, Emeralds for 50gp. Each sell for over 1.5k on the GE, making it a good way to get a quick buck. You will be logged out by the servers if you keep hopping this much though. If you are lucky and the gems arent sold out, you can make well over 100k in just 10 minutes. Great to quickly build a cash stack if you're just starting off.