The people from the UK, that have recently taught at our summer camp, were all on a tourist visa. Although qualified teachers, none of them had basic TEFL either. Makes one wonder what may have happened if there had been a visit from the PSB?

Indeed!

The way I see it is that ignorance of the law is not accepted as a valid excuse. So, those qualified teachers were in a vulnerable situation. The same is true of any foreigner paid by a Chinese employer for teaching lacking a relevant work-related residence permit that does not pertain to the workplace's location.

The problem is a heavy fine and mandatory banishment, probably of 3 years' duration, and possibly a lifetime ban re future employment in China is too big a price to pay for teaching illegally.