Here's an old post that, I think, was originally started by San about fitting for "flat butt" syndrome. It's also a hilarious read because it highlights how the meaning of a word can really vary depending on where one lives. Angie can't stop laughing at her interpretation.
http://youlookfab.com/welookfa.....annie-here
As Diane indicated, the correct procedure for doing this kind of adjustment in RTW pants is a bit more time consuming than just taking in the side seams to get rid of a bit of poof on the side seams. If the tailor's response is something like the following, you know you've found a good one:
Well, I'd take take a bit in on the side seams to get rid of some of the excess on the back, but I'd probably also need to take apart the inseams at the intersection of the crotch to get rid of some of the excess there. I might also need to adjust the dart length and width and/or lift the waistline at the centre back.
By the way, my husband has this done on all his dress pants and is never charged extra for the alteration! So unfair!