Perhaps I'm a sucker, but I tend to buy jeans too long for me and then end
up not getting them shortened because of potential ruin of the bottom hem.
I'm aware of a number of tailors in Los Angeles (inevitably) that
specialize in shortening jeans. Does such a thing exist in NYC as well?
Gothamist can sympathize with the jeans that are too long. We wonder sometimes if the jeans at some stores were designed for Amazons, and not for those of us with shorter inseams. (We'll spare you the rant about how women's jean sizes are totally arbitrary.) And if you buy those jeans that are too long, they either bunch up around your ankles or they drag on the ground and get all frayed and dirty.
We aren't aware of any tailors in the city that specialize in just jeans (if the readers know otherwise, by all means correct us!) but many tailors will shorten your jeans. Manhattan Users Guide and New York Magazine both have some good recommendations for tailors in the city. (And, for those of you in underrepresented neighborhoods, we found this guy in Inwood who will gladly adjust your hem.) We suggest calling ahead to be sure that whoever you choose doesn't specialize in, say, wedding gowns, because it might be a little awkward when you walk in there clutching your new jeans.
We also Googled for more info and found this page from the Vogue Australia forums with lots of suggestions for getting jeans altered (including how to measure the inseam to make sure not too much gets taken off the bottom).
Related: Ask Gothamist on returning jeans to stores with lenient return policies.