Okay since apparently everybody in this thread knows nothing about what they're talking about >_>
In RSC level 10 was less experience than level 10 in RS2. When RS2 came out, accounts that were created pre-RS2 transferred over (all skills, exp, items etc) and the characters that hadn't gained HP experience equal to or greater than the amount of experience required by level 10 in RS2, were leveled down to level 9 HP.
Most people prefer the account to have 1 all other combat stats, but 9 HP is pretty rare. It's feasible somebody might pay $10-$20 for it, but if you have one that is level 1 all other combat stats you'd get a lot more for it.