I'll vouch for Prepare. People take caution to new members and in all honest it should be you going first to most members here as most members are legit. To ensure yourself, just look at their vouch threads, rep, and so on.
I don't scam. Many, if not all members, can vouch for that. If the achievement gives me 1,000 GS I'll pay you the $11. If it doesn't, I'll pay you $5. Deal? Let me know if you're interested. If not, good luck getting it sold.
Scammers usually say they don't scam, don't fall under peer pressure. If you don't want to go first, simply use a middleman.
Also, this won't give you 1k gamerscore.