Just by looking at a Coach bag from a pic that it is really real?
You need to take the time to study the line as much as you can either in person or by reading the authentication thread here.
Do you know if Coach would be able to tell you if something is Authentic by the serial number?
I would say the best thing to do is look at the botiques and the outlets if you have a chance. Look inside the bags, and pay attention to the little details, even smellin the purse. ( I know, that sounds silly, but I speak from personal experience on that one. I bought a wallet of eBay that turned out to be fake, and it smelled like sulfer, not leather.) Geting catalogs from Coach helps alot too! That will help you "brush up" on your skills when it comes to spotting a fake. I'm by no means an "expert" but I am getting better at spotting fakes when looking at them on eBay.
Sometimes the serial number is not enough -- that can be faked.
It really takes time to become knowledgable about the brand. But you can do it. And it's great that you want to be discerning rather than just settling for fake trash.
I absolutely agree, on the smell! Mine is left in a room or in the car and the whole place smells like leather. Love it!!!
I think it's all the extra details that Coach puts into their bags that alot of the fakes do not. I saw a legacy satchel on Ebay. It looked pretty good, but two things made me worry. 1. They were asking $50 less than retail (if its a sold out bag, high demand, why sell it for less than retail?? 2. The stitching wasn't the same. Look at a picture from the Coach website and the Ebay site - side by side (enlarge it). Look at all the small details!!! Each Coach bag in the series is made the same just with different colors!!