The following are a easy and proved ways to make good money in the game Runescape.

Luthas
In the west of Draynor village, go to Port sarim. You will see people in blue uniforms, ask one of them to go to Karamja and pay 30 GP to them. Once you get there, leave the dock and you should see a house. Enter that House and speak with a man called Luthas, who will ask you to pick bananas.
Answer Yes and pick banana, pu them in the crate and then speak with Luthas to collect your moderately earned 30 GP. If you want more money , ask Luthas to get another 30GP for doing the same job again.

Wilderness giant lesser demon
Go to the end of the wilderness where you will find a giant lesser demon, but dont attack him. Walk past him, hang around, after some time has passed he will tell you he is very kind hearted and just hangs around because everyone says he is ugly and scared of him, and because you were brave and not afraid we will give you 150k.

Coal certificates
Once you get to level 30 mining, Go to the Barbarian Village and mine coal there until you have at least 300 coal. Then turn those 300 coal into 60 coal certificates so you can sell them in Draynor Market in World 1, this market has many people buying and selling certificates. you can trade 5 coal certificates from 500 GP to up to 1000 GP each. You can also this certificates in Varrock Marketplace.

Steel Maces
Kill monks in the Chaos Temple and take the Steel Maces, Then sell the Steel Maces in Falador at the Mace store for 138 GP.

Selling droped lobsters and swordfish
Head to Karamja island, to the place where people fish. They fish lobsters and swordfish more than they carry, and will drop the lobsters or the swordfish. Take as much of the fish as you can. make them into Certs in Draynor and then sell them for about 2.000 GP each.

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