Oh, boy...while I have had overall very good service from S&W, I have had one experience that was completely hosed up...and it involved rebates.
A few years ago, when S&W was offering $50 or two free mags with a M&P handgun purchase, I bought several M&P handguns during the qualifying period. I sent in the forms, with receipts, electing to receive mags instead of the money. At the time, S&W had a vendor that was managing the process, and they had an online system where you could check the status of your rebate. The system noted mine as received, but it never progressed from there. Others here who sent in their forms after me were starting to get their mags or their checks, but mine was still showing only as received, not processed.
I called customer service a number of times, and was told a variety of reasons for the delay, including problems with the process, mags out of stock, and a couple of times, just "I don't know." This went on for ONE YEAR!

(I'm not kidding or exaggerating, either...it was one year from the time I sent my forms in until I finally got my magazines.)
I spoke to supervisors and managers, and got no satisfaction. I started trying to contact an executive, and found that unlike some other companies, there apparently isn't an executive complaint process at S&W...the managers said they would refer my complaint, but wouldn't give me names or numbers of anyone I could contact. I couldn't find out any information online about the executives or officers of S&W, other than names. Finally, I happened to find the name and e-mail address of a VP of Finance of a subsidiary company of S&W, and I figured it couldn't hurt. I really didn't expect a reply, or any action...after all, she wasn't even affiliated with the gun company, and I figured she'd just delete it as not relevant to her.
The next day, I got an e-mail back from the VP, asking me to call her...I was shocked, but did so. She asked some questions, got my contact information, and promised me she'd personally contact an executive in CS. The very next day, I got a call from (I can't remember his name now) a director in CS, and he said he would overnight the magazines I was due, plus some extras...he just wanted to know what calibers I wanted (I had bought both 9mm and .45ACP handguns) the mags to be. He followed through, and I got my magazines at long last.
As I said, S&W has had generally great service, IMO, and has even sent me base plates, screws, and other small parts for free. This one experience was outside the normal experience I've had with S&W, but it was completely and totally messed up.