In answer to the question, do I try to sell these pics to the owners?

I approach people, admire and ask about their dog, ask if it's okay to photograph the dog, give them my card, and offer to send them the (400 x 600 pixel) "snapshots" without any charge or obligation if they send me an email to let me know they're interested.

On the back of my card it says that I'll send them "snapshots" without any charge, but if they would like the original digital files to make enlargements, or if they would like those files post-processed, they're available for a very "modest" charge.

To date no one has taken offense, refused permission to take pictures, or otherwise reacted negatively to my approach. Several people have sent emails requesting the "snapshots," a couple have asked for the original digital files, and one person has asked that I come to take pictures of her and her dog (which I haven't been able to arrange to do yet).