Yes, yes. I know the legal fiction. You can find it well-described at
https://www.law.cornell.edu/wex/forfeiture.
But my description of how it actually happens is still valid. See https://www.washingtonpost.com/news/wonk/wp/2015/06/30/why-t... for a recent case where exactly this happened. And it links to 3 other cases where money was seized from travelers, with no criminal charge ever being filed against anyone. In all 4 of these cases a person tried to board a plane, TSA finds money, seizes it, sues the money, and no case is made against the person. In none of the cases did the person get said money back. (The main conflict over where it goes in most cases is that a couple of dozen different government agencies argue about how to divide it up.)
The most unusual trait connecting these cases is that there was publicity about it. It happens so often that reporters usually don't bother to write about them.
The problem is that legal standard is that the government merely has to establish "reasonable suspicion that there was a crime", while the person has to establish "a preponderance of evidence that there was not". This reverses "innocent until proven guilty." How do you establish a preponderance of evidence that no crime happened when no specific crime was ever alleged? It is effectively impossible.
This story from a year ago on the front page establishes the shift in standards quite well: http://www.economist.com/blogs/democracyinamerica/2014/02/ci.... A quick summary is that a couple was indicted of a crime and successfully defended themselves. In the process the government seized a home through civil forfeiture, and the forfeiture stood because the couple was unable to prove that the crime did not happen.
(Unlike the cases that I'm describing above, in this case a specific crime was alleged. Normally the TSA just claims something like, "there was a smell of marijuana" and you have no way to prove that there wasn't.)