I'm bias because we sell on eBay as another way to reach potential customers, but my belief is that if you are dealing with a business that is known outside of eBay then you are probably better off going for them, rather than the eBay only business. My reason for this is that if a business is involved with the automotive industry/culture then it shows commitment and interest to it's customers, thus you are more likely to receive better communication and possibly even a much more customer focused attitude rather than worrying about making a sale and then not worrying about what the customer thinks.
I guess at the end of the day it comes down to your research and by far the strongest factor is word of mouth, as we all know, one good or bad comment about a business can determine 10 or more potential sales. I've probably gone a bit off topic, so I'll just say that its ALWAYS a matter of buyer beware, no matter where you buy from.