If you just arrived in China and are planning to stay only a few days then avoid the street food whenever possible. Your stomach is not used to it.

After saying that, boiled corn is awful to taste but is a safer alternative than some of the stuff they are selling.

As for the saran wrap they have on top. My question always has been `how often do they change it?' I doubt there is any toxic leakage from the wrap to the corn but the bacteria from not changing the wrap for days at a time sometimes worry me.

What the other posters are talking about is `ditch oil'. It is recycling at its worst, they take whatever used oil they can find (at times motor, dirty cooking oil etc) clean it up and sell it cheap.