I see a lot of questions here with inexact code snippets, where the questioner obviously re-typed or summarized the code that's causing the problem. This can make it difficult to distinguish between errors in the original code and errors that the poster introduced by re-typing the offending code. For example, I recently read a question about the behavior of the posted code, but it was missing a semicolon and so would not compile.
The result tends to be that we have to go back and forth clarifying what the real code looks like before we can solve the problem. (Or, in some cases, somebody manages to make a lucky guess.)
In my opinion, we should strongly encourage questioners to copy-and-paste the exact code that they're asking about. Ideally, they should reduce their code to a small, self-contained program that exhibits the problem. If it's a run-time problem, the posted code should be compilable. Error messages should also be copy-and-pasted, and if they refer to line numbers, there should be a comment in the source indicating the referenced line.
If there's something about this in the FAQ, I failed to find it.
I'll usually post a comment asking the questioner to post the exact code, but is there something more general we can do? My suggestion would be to add a paragraph to the "How to Ask" page encouraging copy-and-paste of source code.
I might also suggest a link to Eric Raymond's "How To Ask Questions The Smart Way", though it may be too much to expect most questioners to read all of it.