You have it upside down. More likely that these guys are undercutting Thais and not fairly competing. That's what happens when you flood the market with underpriced services and products. You also can't trust people who do such things, they're more likely to misrepresent things and not honor their word. That's why we have strict immigration laws about work permits and visas. Anyone who wants to knows you can negotiate prices with the Thai tour operators. They are absolutely not "overcharging" unless you don't know enough to negotiate. If someone doesn't negotiate, then they are ok with the price and they pay, so nobody is losing business because of overcharging. I've never done business with anyone but legitimate tour businesses. If someone wants to run a legitimate business they can take the necessary steps for operating a business in Thailand. If they cheat the government then they're more likely to cheat their customers. The whole point of this is whether these vendors are operating legally, which is doubtful.