If a teacher reaches China with a Z visa, things aren't cut and dried. In many cases, the school will assess his teaching within the 30 days that his Z visa can be replaced by a Residence Permit. Remember that a satisfactory medical report and a signed contract along with the Foreign Expert Certificate must be submitted to the PSB for the Residence Permit to be issued.

I put it to you that not all schools that ask Westerners to come to China on L visas are dodgy. If a foreigner does a runner, or doesn't arrive because he has deceived the school by choosing another one, or goes home early for personal reasons, illness or family illness in his homeland, or is fired, a public school is most likely to treat the replacement foreign teacher with his L favorably.

As for teaching illegally on an L, it is just as illegal if you're asked to teach before your Residence Permit has been issued, even though you're holding a Z visa. And many schools will ask you to do the latter. I guess if you refuse, you won't be doing yourself any favors, as you'll be regarded as an awkward employee. And it's a fact that medicals in developed countries are more thorough and much more costly than those in China. Why should you be expected to do two medicals, anyway? If you arrive on an L, you need only do one, the cheaper of the two. But of course a visa run will probably be required later.

Finally, better to be dismissed on an L than on a Z. You can take another post in the province you're in or indeed in another province, without a bad report accompanying you there! I've been dismissed from one place and had good reports from others. It's NOT a level playing field and the Chinese are not to be trusted. What one school says is bad teaching another school will accept. However, what you can do is only apply to public schools. There are still some bad ones, as employers of FTs, but most of them are reasonable employers to work for.

The most important thing isn't the visa type, but to choose a good public employer, even if you have to use a recruiter to find one! There are indeed some agents who will place you in public schools too. That's not a bad way either. Choose the most reputable recruiters and agents if you can't get a public job offer direct.

Anyways, let's hope we can all land jobs working at good public schools in terms of how they treat their FTs, be they as a result of direct employment or via reputable recruiters or via reputable agents.