I received an answer to my question which I thought was poor quality, the user has commented back, and Im trying to explain why I think his answer isn't good.
Can someone with more experience on the site let me know if it is indeed a poor answer, or if I'm wrong. Perhaps someone else can explain to the guy how the site works better than me.
For one thing I think I'm personally very biased against his suggestion, so maybe someone else will see it differently. I'm not sure.
The answerer was trying to be helpful and suggest an alternative to your proposal, rather than commenting on the actual request. So in a sense it is poor quality, but it isn't the sort of answer that needs moderator intervention. That's what the downvote option is for - for stating that the answer isn't helpful.
Flags are for more serious issues. For example:
Not an Answer: This flag should only be used when someone answers a question with something like "I also have this problem, what is the solution?" (i.e. not even an attempt at being an answer to the question).
Very Low Quality: to take the official summary:
This question/answer has severe formatting or content problems. This question/answer is unlikely to be salvageable through editing, and might need to be removed.
This answer does not meet that criteria either. It is well written, and can be salvaged by bringing more inline with the question.
So in summary; answers that are on-topic for the question, but veer off into a direction not requested are the sort that should be downvoted (and commented on - which you did).
(I have cleaned up some of the comments there though. Because while the answer can stick around, some of the comments were unnecessary and argumentative).
JonW already answered that well. But to provide some more background:
A flag says "Dear moderator, please do something about this, we don't want this crap around". There are cases where it is very clear what should happen, for example when somebody posts spam.
But then the question comes: what should happen to answers which are incorrect, such as somebody stating that "water freezes at +250 Celsius"? If you have the requirement that moderators keep untrue answers or bad solutions to your problem from the list of answers, you automatically need moderators who can judge the factual truth of each answer and always know the best solution for everything.
As this is an impossible task for any human being, it is not the moderators' job to remove factually incorrect answers. If the community knows that they are incorrect, it will downvote them, the low score serving as a warning to readers not to rely on the answer. Of course, this mechanism is not foolproof, because the readers are not ultimately capable of judging absolute truth either. But it tends to work for most cases.
If you receive an answer which you think is a poor solution to your problem, you can downvote it. Flagging as "Very low quality" is counterproductive, as the flag will likely be denied. Moderators even have a denial reason when handling flags, which says something like "flags should not be used for factually wrong answers".
JonW already explained what the "low quality" flag is for, but for completeness: use it when somebody posts something like "fdsfdsfdsfds" to your question, without even trying to answer. Then the flag will be valid and the moderator will delete the nonsense.
