I mean, yes, I would hope they have the right paperwork? E.g. if you're going on a business trip then you're going to need a visa allowing business trips, if you're going to work you're going to need a visa that allows work, etc. I don't see why this is unreasonable.
If it is unreasonable then the rules need to change - no point having rules if they can't be enforced.
B1 visa (the 'business trip' visa):
> A B-1 visa may be granted to specialized workers going to the United States to install, service, or repair commercial or industrial equipment or machinery purchased from a company outside of the United States, or to train U.S. workers to perform such services.
So on the face of it you'd think a B1 visa would be sufficient here.
Go read Federal court cases and see how much they have to extend 'good faith'. You can't strictly enforce systems on people, it doesn't work. Even Federal courts recognize this and have to extend 'good faith' to Federal officers and trust intentions versus strictly following the rules.
If it is unreasonable then the rules need to change - no point having rules if they can't be enforced.