If you continue to be vigilant, you should not have a re-occuring problem. As I mentioned, we trapped over 2 dozen mice ourselves last summer. We also had several nests in the insulation of our unfinished basement. After following the above recommendations, we saw 2 mice earlier this fall in the garage, but none penetrated into our home. As far as trapping and baiting go, here is what I learned.
Mice are smart.
Eventually, though, the mice learn to avoid the traps. They will leave an appetizing piece of bait alone because they have seen what happens to foolish mice who take the bait. This was the point where I brought in the professionals. I was worried about poisons because of two small children and two small dogs. The poisons used by pest professionals are wonderful.