I do good deeds, but after I ended up only being used for my money, when I over and over helped a now ex-friend in need with something, I have become more cynical about people's intentions... which is kind of sad as I was cynical enough as I was, before that experience, that I suppose was rather naive of me. I guess you just HAVE to assume that you will get used, in the end, if you show too much kindness. However, I still let others cut me in lines, I hold up doors to completely random people, and I am very honest if I buy something from a smaller company, and they end up charging too little (or returning too much, in the case of returning goods for the money back), and I always buy some things I need from a smaller store, where I live, since I know he doesn't get that many customers... and he's a kind person who acts respectably, anyway. I have also ended up helping an elderly lady with her bicycle lock, since she couldn't get it open, due to not having her glasses, or something... she became very happy. Of course, before you do things such as that, you have to realize that the person may be a pickpocket, so you should not let your guard down, and be aware of assistants being around to that possible pickpocket. :/ Definitely check your pockets, afterwards... -_-
I personally just do it because I feel it is the right thing to do, although I guess being kind to random people helps me feel a bit less dead inside, as well... however, I am a very peculiar person, as if someone treats me even mildly poorly, I may start thinking about acting out in revenge against them, or if it's very poorly, I may start feeling murderous. -_-; But if people just are polite and kind to me, I will be at least as kind and polite back to them... despite the fact that I know that if I knew them better, I would most likely dislike them rather a lot... but regardless how few I would like, and how few would like me, I have to meet them with a default goodness - no matter how few you'd at least somewhat like are around, they still are there, somewhere... and even if you kind of would disregard that they are there, it's otherwise so that if people would all act impolitely, due to their assumptions on who they wouldn't like, it'd only be war in this world. So a default kindness to people you well may even hate is the best way to handle it all... and at select few times you may even find that the people you thought you would hate aren't so bad, after all.