I thought most people pulled apart a new gun and cleaned them.
Lol. If I am truly interested in a firearm, in this case a pistol, and intend to buy it, I pull out my concealed carry license throw it down and tell the salesman " if it meets my inspection I'll buy it now" then I proceeded to field strip it on the counter, right in front of them, boy, you should see how many guys just grimace in concern when the slide comes off and springs come out, you'd be surprised at how many people sell guns that have absolutely no idea how to do anything with them other than rack the slide and check the chamber to show it to a customer.
To OP
What a bummer man, I feel your pain and frustration. One time I bought a new firearm I took it out and put a box of rounds through it and brought it home to clean and inspect. Took it apart and the tolerances were so tight the slide would not go back together with the rail, in fact, I had a hard time getting it off, after some sanding, light filing, and an ample amount of gun oil, it slipped together nicely and has provided me with 1000's of maintenance free and accurate rounds. Since that purchase, I field strip every pistol I buy, before I buy it. I spent several tedious hours trying to get that gun together, hoping I didn't screw it up with every stroke of the file, I guess I could've sent it to the manufacturer, but that's not really my style. In your case, I don't know what I'd do, shitty deal for sure, sounds like S&W is gonna take care of you though. This gun is for your wife? Did you check out the Kimber solo, beretta nano, Springfield xd-s? We got the solo for my wife, she's a petite little thing she's not a "gunny" but she is comfortable with it, it fits her hand well, it's light, and she shoots it accurately. Just food for thought, in case you decide to try and return the S&W.
Good luck