| Look at it this way:
If he limps in and then goes all-in AFTER you've raised from the big blind, he's most likely looking to gamble - because he's putting you on a solid hand but thinks his pair will hold up if face cards doesn't come up on the flop. Generally, when good players do that, they're either holding 10s paired or above, or AK suited. At worst case, AKo. If he had small pair, I'm sure he would have either re-raised you 2x to see the strength of your hand or flat out call your raise to see if he can make a set.
In this case, it was not worth it to call such a big pot with A9s. Too many variables can beat you.
At that point, save your money, fold the hand. I wouldn't call that hand unless I had a genuine hand like 10 pair or above or AKs. Because it will leave you crippled. | 
