Where can I find the most reliable place to purchase and sell old school Runescape gold?

I'm more of an individual buyer than a seller, but my preferred source for RuneScape Gold trading is the RSorder. It's essentially a trading site, which means that you're neither purchasing or selling through the company, but through independent traders using their system.

Here's what I believe are the benefits when doing business directly through a business:

Increased competition between sellers push prices down

They are not able to make any kind of charge they wish.