Well, as far as I know, selling a game that you have already finished or got bored of and don't play it any more, it is legal to sell it so yeh, my answer is Yes.
No, it's not, pls refer to my reply at the end of this thread for more information.
"Blizzard does not recognize the transfer of Accounts. You may not purchase, sell, gift or trade any Account, or offer to purchase, sell, gift, or trade any Account, and any such attempt shall be null and void."
Trading (or selling) accounts is not allowed here as per the SteamTrades site rules.
Also, read this quote from Blizzard's (Diablo 3) Terms of Use:
"Blizzard does not recognize the transfer of Accounts. You may not purchase, sell, gift or trade any Account, or offer to purchase, sell, gift, or trade any Account, and any such attempt shall be null and void."
And this quote is from NCSoft (Guild Wars 2) User Agreement:
"NCSOFT hereby grants You a revocable, non-exclusive, license for personal and non-commercial use of Service, Content and Software that is non-transferable except as permitted under Section 9(c)."
"Each Account may only be used by one person. If a minor has been allowed access to an Account under Section 9(c) below, only that minor may use the Account thereafter. Except as provided in Section 9(c) below, You may not make any assignment or transfer of rights, obligations or liabilities related to this agreement and any attempt by You to do so is null and void. "
Thank you sir for replying, as long as you are not intersted in the product i sell, i will take your reply as innapropriate. I am still waiting for users interested in my products.
The only inappropriate behavior here is yours. You're breaking the rules/terms of Blizzard, NCSoft and most importantly SteamTrades.
I Trade them for TF2 Keys or gifts worth the same amount as the keys.
Diablo 3 - 10 TF2 keys
Gw2 (Guild Wars 2) - 10 TF2 keys
Add me on STEAM if interested.