I felt like I was in Tijuana yesterday afternoon! A man and his child were selling from seat to seat. The kid had a tray of random things from gum to bracelets, and the man had CDs, DVDs, fake Giant/As pins, caps and head bands in his tray for sale.
They were non-threatening so I didn't bother to get up to call the TO. It was actually kind of funny that they were doing that on the train.
I see people selling things outside of the stations but rarely inside the train. I've seen people begging or performing on trains, but not actually carrying around a selection of random trinkets in a tray and asking people to take a look.