The last time I so much as questioned an american customs agent about something they asked me to do, I was interrogated for 2 hours about my life, job, friends, family, phone searched, car flipped through, etc.
They even had 2 canine units circle my car and jump in and out of it at least 10 times each.
Some people get off on power, and this job is as close to having power over people as some can get.
As long as you know you're not actually carrying contraband or is a terrorist, just smile, comply when reasonable, and then say politely that you'd like to see their manager to file a complaint.
I travel across the US Canada land border from time to time (in the mountain west). My experience has been that Canadian officials are universally civil and respectful while US officials are universally not.
As a frequent traveler between the US and Canada, I’ve only ever got grief (including accusations of smuggling) from Canadian officials. Going to the Us side it’s usually a simple “have a nice day”.
They even had 2 canine units circle my car and jump in and out of it at least 10 times each.
Talk about a heavy handed approach.