Crap. I had a long response typed up and hit post but somehow it didn't get posted and I lost the text. (Edit: it got deleted for being inflammatory, which, admittedly, it was!) In any case, to summarize what I had written, minus the flame:
If you're going to offer advice, like Puspawarna and Jamie C did, then offer advice. Note to potential respondents that the work may be illegal without a work permit, and to consider the risks of being visible in a media appearance. If you think something is illegal or in violation of forum rules, report it and let the mods decide whether or not to delete it.
Offering veiled threats such as MadCat's original response are condescending, unhelpful, and emotionally charged.
Despite what some of the responses in this thread seem to imply, the law is a sliding scale that can hardly be said to be black or white on anything, especially in the areas of enforcement and punishments, and legal risk is just another risk that normal human beings have to consider when they are going throughout their daily activities ("well, crossing the street here would be illegal jaywalking, but the traffic is light enough that it will be safe if I time it properly, and even if a cop sees me he probably won't mind as long as I do it safely").
I have already granted in a previous response that the OP is asking about illegal work - but it's hardly in the same line as an ad titled:
"English teaching position, 30 hours per week, 10jt per month salary. NO WORK PERMIT PROVIDED! Details inside..."
At some level, you have to be willing to let others make their own decisions and decide for themselves how they feel about the potential risks involved.
Unrelated note / snide comment (small flame): I'm glad to hear that sales isn't labor, so if I take a full time 40hr/wk job in sales and they come check for my working papers, I'll just tell the police "I'm in sales, it's not a real job." Hahaha.....