IF you are very used to growing particular strains, you can sometimes identify those plants on sight, IF you know what the possible choices are. Like if someone had 5 strains in a tent and I was familiar with all, and I knew there would be no other odd strains in there, I could probably ID them accurately.
But there are thousands of named strains and millions of crosses. And the gene pool for Cannabis may not be very deep. A lot of plants look the same. It would be a shot in the dark for me if some random plant was presented to me.