It's done this to me before. It may have something to do with the passives on Demon Hunter (presuming that's what you are). I just got on mine and looked at some items in-game: without Sharpshooter, they would be -6.5k, -12k if I used them. With Sharpshooter (at 100%), they changed to -12k and -14.5k. From the Auction House interface those same items showed at -5.5k and -10.8k without Sharpshooter, and -5.7k and -11k with Sharpshooter.
If you have Lyndon or Eirena with you and took their crit/attack speed auras, that could further skew your numbers in-game. With Eirena as my active follower with Focused Mind, the numbers in-game went to -6.7k and -12.5k without Sharpshooter, and -12.3k and -14.9k with 100% Sharpshooter. The Auction House interface numbers stayed the same as when I had Kormac selected.
possibly something to do with crit and dex. that with the buffs you have ingame make dex more worth than crit. And since you didnt have those buffs in the AH it showed the crit helm as higher. And ingame when you had buffs. the high dex was more worth in dps