You'll find no shortage of people wanting to negotiate with you if you are consistently willing to give up negotiating leverage for feeling good afterwards. In the case of the trinket vendor, they won't spend a second thinking about that one tourist who negotiated better or worse than the other hundred tourists that day. There is nothing intrinsically wrong with charity, but I don't think you should delude yourself into thinking it's anything other than that. Personally I can think of other causes I find more deserving than trinket vendors in touristy areas but whatever floats your boat on that.