In the days of yore, (C. 2000) there were rumors that if you bought a gray-market watch from the internet, it would have the serial-numbers filed off. I never saw this, nor actually saw a post by someone that had, it was more "be careful, my friend said this one time...." I don't know if it ever happened, but I've never seen it, nor has anyone posted anything to that effect recently. As for value, I think that a GM watch can sometimes hold it's value better, as there isn't that initial depreciation from MSRP to market, so even if a GM watch sells for a few % less on the secondary(not saying that it does, but even if) the drop is still smaller. WRT boxes and papers, it depends. Some dealers never have them, some do. I think most would fall in the middle, having BP for some, and charging less without them.
As for authenticity, none of the reputable dealers would ever knowingly sell a fake, the risk is too high. Someone with a store, or even severl years of history behind a website is not going to blow that commercial good-will on a fake, the risk is too high and the cost too great. We can't discuss dealers here, but there are forums where that is possible, or ask for references via PM. I know people have their favorite dealers, and would be happy to suggest.
Aaron
This time the pictures are of a American Private-Label. The mvmt looks like a patek, but sometimes it is hard to tell. It was in the collection of a local GM, but has been sold.