What is the best visa type for a US citizen in Thailand when overseeing operations at a factory without a legal entity?

For a US citizen planning to oversee operations at a Thai factory, the only suitable visa is the Non-B visa, which requires a valid work permit to legally work in Thailand. It is crucial to obtain these before arriving and to avoid working without the proper visa, as this could lead to legal issues, including detention or deportation. Border runs can extend stays but do not authorize work. Companies should ensure proper visa arrangements for employees to avoid legal complications.