I'd add a few steps to your, already good, list. First, if possible why not simply ask? Just a few days ago I was in a pharmacy in a remote area of a tropical country and they had a really beautiful collection of old glass container they use for raw material which looked like a chemistry lab from the 19th century, I told them I liked that and asked whether I could take a few pictures, I promised them to send them some small file and told that I could give them one print if they wanted, I also told them that I didn't have any plan to use the images for anything commercial but that if occasion would arise of course I would ask them their permission. I toke many pictures, and while I was taking them another guy, probably a tourist, toke out his camera but the reaction of the owner of the pharmacy was to tell him not to take pictures and explained that he was letting me do that because I asked, explained who I was and could trust me. The second is about getting caught in a closed area, I think that if you are in some private property and a ward get you in many countries they have the right to confiscate film or memory card (I am thinking of places such as those visited by "urban explorers" such as abandoned building, factories, destroyed constructions), in this case I would consider a quick change before they get close enough to notice and handling to them an unexposed film/empty card.
GLF