All Runescape accounts are recoverable.
Even accounts that have never been a Member can still be recovered, although it is less likely. Any account trading is done at your own risk. Always ask for membership information and it's best to always trade experienced, vouched members.
Check the RSN Scammer
list to make sure the account hasn't been sold and recovered before. If you do buy an account and it gets recovered, report it in the same thread.