I've taken my Jaguar and Mercedes to S&J many times. I don't get all the one-star reviews. No, the diagnostic charges aren't free, nor should they be. Diagnostic equipment can run $10k+ for just one make. But they apply the diagnostic charges to the cost of the repair, which is fair.
As for the other negative reviews, I don't know what to say, except consider the source (a mechanic from Craigslist fixed the problem when a Bosch-certified repair facility couldn't find it? really??). Seriously, don't believe the hype. A garage is not a charity. But some of these reviews lead me to believe that people think it is.
Bottom line - these guys do great work for a lot less than the dealer charges. The staff is friendly, the lounge is comfortable with free wi-fi, and they've even shuttled me around at no charge.