I generally try to stop and heal people when I'm running around and see someone who needs a heal.. I have had it backfire on me as well though, with people suddenly pulling far more mobs then they can handle and expect me to heal them through it.

Back in FFXI I was helping a group in Valkurm who had lost their white mage, keeping them healed while they waited for the new white mage to arrive (I was a high level white mage at the time). Other people saw it and thought I was power levelling that group, and I got several tells from people asking if I could power level them as well. I declined, and after a while I get a tell from a GM saying I had been reported and he was investigating. Turned out 1 of the people I refused to power level had reported me, go figure