For me, personally, while "Joe's Truck Parts dot com" might do a better job of finding me the floor mats that fit my truck (or the manufacturer) - Amazon already has my credit card on file, and my address, and (for the most part) ships anything I order to my doorstep within two days. So I know I'm not transferring my credit card data to some random, sketchy company who stores it on some Windows 98 server, and takes 2 weeks to ship me my product, and when they finally do ship it, it could take 7 days to get to me.
In either event, I do like to support local business and small business - but I enjoy the convenience and familiarity that Amazon offers...so even if their search isn't the greatest, I'll still be clicking purchase on their site, for the most part.