Involuntary upgrades are beyond the control of the pax. How do they relate to your potential of being a smuggler or tewwowist or having a banana in your bag? :confused:

I traveled to Mexico many times this year for work 3-8 day trips and almost always carried-on. As luck would have it the one day I checked bags I got a new agent in training that sent me through a USDA inspection and my bag was lost-actually, I suspect someone else grabbed my bag-Travel Pro 22” suiter and dropped it off for re check after customs. That caused an issue as I was ‘obviously’ hiding something.

In this case it was a training exercise that caused the extra screening.

There is ATS-trigger selection and then there is the individual agent(s)' "I don't like you/your answer/your look/etc"-trigger-type selections.

I once had a load of luggage in a luggage cart in YYC, handed my customs card to the Canadian customs agent, and she said "you don't have any luggage"? I pointed at the cart I was pushing. "Oh".

Yes, it is a trigger unfortunately.

My ex- got isolated out when she traveled home separately from me. I was on a business assignment in GVA, she came for part of the trip. Most cost effective way to get her ticket was award travel on a partner airline, so we came back separately.

There were, apparently, some odd looks by the Customs folks as they ransacked her bag and found it full of dirty underwear for the both of us.... I brought the rest of the clothes with me (better baggage allowance).

I'm a brown-skinned guy who's noticed something when I get the secondary screening. I find that when asked to submit to a secondary customs screening - it's usually the officer that looks a little like Farva from Super Troopers that sends me over - every airport customs line has one. I do my best to avoid that line. They seem to send me over more than the others do...

If you travel to countries like Colombia customs agents will be more vigilant.

Like most law enforcement officials, customs agents look for things that are out of the ordinary. This would include someone not having the usual amount of luggage for the trip, someone traveling on odd itineraries, etc. I don't think there is much you can do about it. You can't increase the size of your bag due to carry on regulations. Just note that you pack efficiently if they bring it up. There's not much you can do about it.

"If you travel to countries like Colombia customs agents will be more vigilant."

Lets just say, if you make a one day trip to Colombia and are carrying several large suitcases, be prepared to be in customs for a while ;)