Take this to the grave when buying accounts. No matter the site, the method, the amount involved in purchasing a Runescape account it can always be recovered. No matter what information you are given, and no matter the assurances, you will always be vulnerable to a recovery.
If you're wanting to buy an account, forget the different websites and such, buy an account of someone you can fully trust, and know that recovery would never occur. Such sellers are on Sythe (IMO), they are, Video, Snow Patrol and KMJT. Look them up, and you'll see they've sold accounts totalling over $50,000 (in particular Video).
Personally, If you're after an account that will always be yours, bot it.