Valve has requested the developers taking part in the Greenlight program no longer offer game codes in exchange for votes.
In an announcement from Valve, the post is locked but Steam Database posted it to their Twitter account, the company explained the reasoning for their request.
When you give away copies of your game in exchange for votes, you put us in a really uncomfortable position. We do not think these votes accurately reflect customer interest and it makes our job harder in deciding which games customers would actually buy and play on Steam.
Valve is asking developers to no longer promise keys for Greenlight votes. pic.twitter.com/8v5zCdEhyl
— Steam Database (@SteamDB) February 10, 2015