I'm not talking about Thai schools either, free or not. Quite frankly, I wouldn't put my dog through a Thai school, they are absolutely awful.
Yes, there absolutely is a way to guarantee a minimum level of training and certification, every heard of the PGCE system in the UK. Every PGCE provider has to teach core subjects, and every participant has to attend a school placement for a minimum of 24 weeks.
Your point about schools in Thailand having teachers without teaching licenses, I can guarantee that any international school worth it's salt would never dream of employing a teacher without a home country license. I am talking about KIS, Bangkok Patana, Ruamrudee etc.
Look dude, TEFL teachers have their place, they can provide a good service to Thai schools and the Thai curriculum. But, they are not qualified teachers, and thus they shouldn't be remunerated in the same manner as qualified and licensed teachers,