You should know better mate. Provide us some stats for breakdown of source traffic, some charts for uniques over the last few months.
Ideally you should give us screenshots or, even better, guess access to Google Analytics or Statcounter projects. Even if you don't use either, you can show us AWStats or something similar from your server.
You need to reveal more because right now you could be hiding something. And, as someone else mentioned, why such a low multiple? Yes, it's black hat/illegal - is that why? Why aren't you asking for 10x or 12x monthly income?