I learned a new Italian word on this trip - ritratto. It means portrait, and it's what I would ask my subjects for rather than a photo. I don't know if it improved my success rate, but it at least sounds less intrusive and confrontational. All were locals of Venice or the surrounding towns except one. The Japanese girl I spotted several times on the island of Burano. She had a small tripod with her phone mounted on it, and would find a likely location where she would spend several minutes snapping selfies. After we crossed paths for the third time, I couldn't resist asking for a photo (no ritratto this time).
So, in order, I present la tourista, il libraio, il mercante di vetro, il pescivendolo, il professore and la matrona.