So folks, obey the visa rules of the country that you're travelling to. If you go abroad with a tourist visa and look for some "under the table" work you will have no recourse if the school stiffs you. In fact, it's a smart idea to obey the laws of the country that you're in. For me, that means honoring my contract and not mounting one-woman protests about aspects of China that I disagree with. For others, that might mean not smoking weed. For some unknown reason, a 24-year-old ESL teacher recently traveled from South to North Korea, ripped up his visa and asked for asylum. He's now begging to get out as he begins a six year sentence at hard labor. Whatever this young man thought he knew about North Korea, it's clear he didn't know enough.
Here is a link to a list of schools in China that have had various complaints lodged against them. I have no first-hand experience with any of these schools and trust that, as the site says, they don't post rumors and they do allow the school to post a rebuttal, much like Trip Adviser allows hotels to respond to customer complaints.
Raoul's China Saloon is an online (natch) forum for ESL teachers and has a thread dedicated to asking for feedback about about employers and job offers. A good place to get help from seasoned expats.
I found my current position through Profs Abroad and recommend it for people looking for a university-level job. You are able to apply directly to the hiring institution, not through a third party. There's now a small subscription fee, but I think it's worth it.
I didn't know there was actually such a thing as snake oil. Snake oil cream is an inexpensive unguent used for joint pain. It's considered to be old-fashioned and only for old guys, like Geritol.