But it gives information to a buyer which helps him knowing the risks
The majority of people are aware of the risks from learning the hard way. Although it may be true the new wave of consumers way not be aware of all risks, there are topics in plain sight identifying them.
Accounts is a risky market, hence why it's monopolised by a handful of trusted account providers. It all comes down to common sense really, which I know is a ballsy statement considering many people don't, or become too tempted by a cheap price.
A lot of things could be changed, such as making stricter listing requirements, colour coded systems to separate "original owners" and "non-original owners" of accounts, etc etc, but the harsh reality is that there is little to no way to prove any claims made by vendors. Again it all comes back to trust, which is built personally between the buyer and seller.
Unfortunately unless Jagex make any changes to their account security system to benefit account sellers, which they won't other than developing algorithms to detect ownership transfer (which they have already), then nothing can be done to secure an account from recovery risks down the line.
Even if the buyer has accurate recovery information, they will lose a recovery war against the original owner. Either the account would become perm locked, or the original owner would get the account back.