bad underplay or bad luck

Was early in a no limit tounement with about 12 tables remaining. Blinds were 15-30 and I have 99 in Early position. BB and 2 others just limp to my raise to 75. Too passive? None of the bigger stacks were in action and no one was real short. The flop was great 9-4-4. Check in the BB so I check trying to trap or let someone catch up?? It checks around and turns an A. I slow play again, thinking that this will be bet but, horrors, another free card. It now rivers an A - ugly and I muck after a middle player bets and the button calls. The "Table expert" says, if you have a hand bet it" but I thought that the slowplay was better as I would have gotten no callers. Even with the turn, the other A would have folded, according to him, because my first check convinced him that I had AK and my kicker was better. Greed got me but was I right to be greedy with this flop?