Is it a good idea to come to China on tourist (L) visa to look for a job teaching English?

It is reasonable to scout the scene before hand. Just be sure that you are one of the nationalities that can go to Hong Kong for a Chinese work (Z) visa. Also be sure that the foreign experts bureau invitation letter is marked with Hong Kong and not your home country. Be aware of the costs of going to Hong Kong and staying there for up to a week. Also be aware that not all nationalities can get their visa processed in Hong Kong, and you may find yourself having to return to your homeland to process the work visa. Don’t trust any school that suggests you can work on you L visa. That should be a big alarm bell that this school is poorly run. Also don’t believe anyone who says they can change your visa in the country. One travel tip. When gong to Hong Kong from the mainland, it is much cheaper to fly to Shenzhen and take a taxi or bus to the border than to fly direct to HK airport.