I'm more than a actual seller, but my preferred source to go for RuneScape Gold is the RSorder. It's basically a trade-between-players site, which means that you're neither trading or buying with the company, but through independent traders using their system.

Here's what I believe are the advantages in doing business directly through a business:

The more competition among sellers drives lower prices

They are not able to be charged whatever they like.

More Community

A wider range of personalized services

I'd say that they're among at least the most secure websites available. The trades are facilitated by an escrow system and when you buy the item, you pay for the purchase to RSorder. They then notify the seller who contact you to schedule the delivery. After the gold is delivered, you have to confirm that you received it via RSorder and they'll transfer the cash back to the vendor (if you do not confirm, they'll release the funds within a couple of days).

Before trading with the seller, you can review the comments left for them by buyers who have previously purchased from them This is a great resource. It's simple to discover who the most trusted sellers are, particularly for RS 2007 Gold.