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