If you want to sell gold be careful. People can simply charge back the payments on various websites such as paypal because they don't protect virtual good trades (has happened to me). Furthermore, keep note of every part of the trade. This includes taking pictures/recording of chat logs, trade, etc. When purchasing gold i recommend doing so by people that are well known in this site for selling gold.
Use your common sense. If they are pressuring you into going first, it is most likely a scam.
Middle mans are people that will often handle your transaction for you. There are OMM which often cost a fee and free MM looking for a reputation, such as myself.
The bans on runescape are not that high. Make a new account in which you can transfer the money onto your main, this is called a mule. That way there is no transaction between your important account and no risk of ban there in case the transaction goes wrong. Any other questions you can pm me and i'll be glad to help.
Good luck trading!