It's morally bad to help a stranger, but it's paid, but is it legal? Is there any legal support?

There is legal support. Because after all, you helped him at the expense of time, opportunity and so on.

For example, some people can ask for a certain reward because they have delayed their important things by helping others.

For example, if you meet a pregnant woman who is in a hurry to give birth on the road and can't get a taxi, it is reasonable for you to take her to the hospital and ask her to pay some gas money.

It's just that this requires the consent of the other party, and at the same time it can't be overcharged, so it's suspected of extortion.

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