In my opinion:
1. If you are providing a legitimate product or service in return.
2. If it is literally a life-or-death situation. For a human, not a pet hamster.
3. You are starting a business and are soliciting investors (though this would usually provide return to the investor by way of repayment or a stake in the company) .
Maybe I'm forgetting something, but any other need or want for money can be resolved through hard work, through loans, or through assistance from family members, government agencies, and other specific charitable organizations.