Just to add to the other responses.

I agree 100% with VancouverMark. It makes more sense to go to a store that specializes in tobacco products and buy cigars that were kept in a humidor than to buy them at some corner shop that doesn't even have them in a humidor.

If you do decide to buy them at the corner store and follow Eville's advice (it's good advice) you want to remember to:
1) Use distilled water
2) Do not over humidify the cigars.

A soggy cigar is not a good smoke. So, if you don't have a hygrometer to ensure proper humidification, take Mark's advice.