What you should do is say, "Sorry, but can you give me more information?" then
explain what information you need.

Don't just rudely say "We're not mind readers". Patronising the user is likely
to make them not bother posting again, and finding another program. It
happens.

Be nice. I don't care if you're the only respondent, friendliness costs
nothing. I work in IT, and if i rudely patronised a customer that asked the
same thing that's been asked 5 times before in the same day, i'm a bad support
guy. And i'm my own boss, so i've got to set a good example, no matter how
tiring the job.

If you can't handle it, then you're in the wrong sector. I've seen how you are
nice, that i appreciate, but not everyone can be bothered trawling through
pages of search results on a forum, it makes you lose interest, depending on
the person.