Ebay can be a great place. I'm not saying anything about your purchases cause you have brought some nice looking pieces to the table here.
I think I'm right in the middle with everything. I think it's been said before, but I cant say it's impossible to make a good purchase online. It certainly is difficult though. So I guess I don't really side with your professor either (like the smilies by the way). The worst things that cannot be seen by photographs are odor, dry rot, and sometimes surfaced warps, splits, lazy stitching, some repairs, foundation and patches. However, with proper photographs of poor areas, the only thing really posing a threat would be dry rot and odor, and in some cases you can see signs of both of these.
I do think there are ways to make margin of error smaller when purchasing online, for example bringing a rug to this forum for review I think can and may make things apparent which would otherwise not be seen in photographs unless a familiar eye sees it. I'm not saying we can catch everything by looking at photographs, but it certainly helps. Most sellers would not go to the point of being decptive and alter photographs, but even still, a lot of these alterations I can catch sometimes. and as the verifications state, its in the best interest of the seller to accurately describe condition, genre and age of rugs.