If you catch a pocket pair, and its lower than, say 10s, You should always consider to call if its not to many high raisers before you.
And yes its a pretty small chance 2 catch trips on the flop 1/9 you catch. But if you do catch you should se yourself as a strong favorit and try to get their money in if its not a very scary flop, like 3 spades and you have 222, you should be a little more careful. Always try to hit'em if its not costs more than 2-3BB i would say.

/Woelle