IMO is would trust a local mechanic as long as they are trust worthy. lol I know that sounds funny, but just because somebody labels themselves as a performance shop does not mean that they are great mechanics. It only means that they are targeting a certain client and maybe that they actually specialize in performance part installation. A down pipe should not be difficult for any seasoned mechanic. I guess bottom line for me is take it to a shop that you consider trustworthy and has a good reputation, not just someone who claims to be specialized in a certain area.
2002 WRX Wagon-Up-pipe, Invidia Catless Bellmouth Downpipe, Stage 2 OTS, Jack-n-the box antenna ball