This is rather sad. You are one of life's put-upons and are too good-natured to refuse. The fact that your reward will be in heaven, rather than on earth, is scant comfort. You come across as someone who would be very reluctant to deny a helping hand, even though you know people are taking advantage. I have no real answer to your dilemma, but as far as the lady who keeps 'forgetting' her purse, I would smile sweetly and say, "If you lend me your key I will pop round to yours and fetch it back for you".