Paul,

I can only speak for China, but as far as I would be concerned, the thing you really need to look out for is that the school has a license to employ foreigners and will give you (and I mean GIVE you to keep) the Z class visa and an expert certificate.
Ask to speak to other teachers at the school (and past teachers if possible) to ask about their experiences and if they had a visa.

If you need any more advice please e-mail me.