"Spam" is defined right there in the flag popup as "Exists only to promote a product or service":
but most of the spam flags I process have no advertising, promotion etc. They are just VLQ, NAA, gibberish, etc.
In an effort to dissuade the spam flag's misuse, I decline incorrect spam flags with a "a moderator reviewed your flag but found no evidence to support it" message, or sometimes a custom message like "I see no advertising here". But it's a losing battle.
Can we add a field to the popup that asks the user to enter the url/name of the thing being advertised?
The idea being that if people are too lazy to read (as evidenced by the statistics), they are also too lazy to enter anything and so won't use the spam flag incorrectly.
It would also help speed the review process, making it faster to identify multiple spam posts from a user or about a product.
Alternate, simpler, proposal... remove the short names!
Admittedly, the amount of spam per day isn't that large, and perhaps this question should be tagged catharsis.