That is indeed a concern, but I've found that if you act in good faith and kindness most of the time, but just throw in a tiny bit of skepticism, you can filter out such abuse most of the time.
It's not a good idea to go though life bitter, angry, suspicious and angry at the world and everybody around you because you fear that someday down the line in many years somebody might exploit your kindness.
It's not a good idea to go though life bitter, angry, suspicious and angry at the world and everybody around you because you fear that someday down the line in many years somebody might exploit your kindness.