Comment by cyberax
> I believe a lot of them were on B-1/B-2 business visas (or equivalent ESTA), which are typically intended for "business meetings", not for "work".
B-1/B-2 does allow some work. Specifically setting up complex equipment and also training workers. Here's the CBP manual: https://www.cbp.gov/sites/default/files/documents/B-1%20perm...
> If the contract of sale specifically requires the seller to provide these services or training, and you possess specialized knowledge essential to the seller's contractual obligation to perform the services or training it may be permissible for you to perform these services. In addition, the machinery or equipment must have been manufactured at a location outside of the United States and you may not receive compensation from a U.S. source.
Now the catch is that people on B1/B2 visas have NO recourse if _any_ border official decides that they violate the visa rules. And the rules themselves are really unclear.
Thanks. I guess it's even more complex than my understanding then, and a matter for lawyers aware of the case law to handle.