I traded with this person 6 months ago, where I gave him a key (Abatron) received in a giveaway that activated as '..for beta testing' - this is common for giveaway/review keys and does not mean that the game will be revoked, as I'm sure most of you traders know. We agreed that I would compensate if it was revoked and moved on.
The game is still in his library, as expected. I sent him a new trade offer, and he accepted. After I sent him my key for the game Rugby World Cup 2015 ($30) - he stated he was unhappy with the trade we completed 6 months ago, and demanded more games before giving me his part of the deal. In the evidence below you can see how he changes his mind in the middle of the trade, steals my key and demands more games.