The decision, while it hurts and may seem "unjust" and even cruel, is nevertheless correct under existing law.
INA Section 214(b) which suspects (and assumes) every visa applicant to have the secret intent of wanting to immigrate to the US is the reason for the denial.
To overcome the Section's "immigrant intent" presumption, one must prove "substantial" ties to one's home country, such as an important, well paying job to which one will have the incentive to want to return to after temporary foreign travel, a good social / financial situation (serious money in the bank, property ownership, etc.)
Once your Friend's situation changes and he is able to overcome the immigrant intent presumption he should apply again. But not before.
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
There is no particular income requirement but one must establish strong ties outside the US that make an only temporary stay in the US likely. Owning property and having a job outside the US are a strong indication that the person will not stay permanently in the US.
I agree with my colleagues, but I would add that despite low income and no property, it may still be possible to get a visitor's visa. Your friend must document other "ties" outside the U.S. Other examples may include enrollment and substantial progress on a college or advanced degree abroad, spouse/children living abroad, etc. If your friend has other strong ties that can be documented s/he can consider reapplying.
You should always consult with an experienced immigration attorney to make certain that the advice you received is appropriate for your particular immigration case.