got answer for possible sale

Taking money for your account is not allowed by OCN or steam. I dont think you can gift games from steam unless you have more than one copy, but im not 100% sure about that. In anycase selling your account as a partial or as a whole is not allowed.

So for an appraisal i would say zero dollars.

It's againt the EULA to sell a steam account.

Yeah, if you got an extra copy of HL2 or any game then Steam will allow you to gift the game to someone else's account (or if you buy a game on Steam you can tell Steam that you want to gift it to someone else). But if it's already on your account and you want to sell that, then it is against Steam's TOS, and therefore against OCN's TOS since it's illegal.

That said, people do it all the time. Not on OCN though, since it's not allowed.