Any site attached to a dealership should be legit, and they typically prominently display on their website that they are in fact dealerships. I've bought from mazdastuff.com before; I think they're a dealer here in Texas. Mazdaswag.com is also a dealer, and I've bought from them too. BAM Wholesale is not a dealer but has decent prices and sells genuine OEM parts.
The only issue I had with mazdastuff.com is that they didn't pack my struts well and the brake line eyelet on one of the struts was bent during shipping. I sent them a note and they never responded, probably because the guy reading the emails was the same guy that packed the struts poorly.
