The teens claimed CBP targeted them because they hadn’t booked hotels for their entire stay in Hawaii.
“They found it suspicious that we hadn’t fully booked our accommodations for the entire five weeks in Hawaii,” Pohl said. “We wanted to travel spontaneously. Just like we had done in Thailand and New Zealand.”
Travel advice to USA has pretty much always been to have your destination/hotel at hand for customs and your tickets for the flight back. They were also interested in how you would get to said destination, so better have a car rented in advance.
In addition, don’t say anything that suggests you will work, even if unpaid. Don’t mention volunteering, helping a friend, doing remote work, etc. The rules are quite specific about what visas allow and do not allow, and many border people are just there to catch a paycheck - they will absolutely err on the side of denial. It is not a fair game, and you will not be given a fair chance to explain yourself.
Turns out it never was a free country at all
It was so silly when the immigration officer asked me (at the origin, not the destination because they want to avoid to fly you back): “And what if John won’t be there to pick you up at the airport?” Me: “I don’t know man, take an Uber?”