I always assume by the time I've passively heard of a fad it's too late to realistically capitalize on it.
Or it becomes the new status quo.
It's easy to think of fads restrospectively once they've already passed and identify them as fads, but a lot of what people assume are "fads" actually stick around.
As someone raised in the art community, I thought cameras on cell phones would be a short lived fad because I assumed that no one would want to look at other people's shitty photography. Now it's the cornerstone of youth culture.
Malcolm Gladwell talks about the example of a small group of New York hipster kids making Hush Puppy shoes ironically trendy, which is the very definition of a fad, and yet it massively blew up the company.
Sometimes a "fad" is actually a "next big thing", but yes, usually by the time you've heard of it, it's very difficult to cash in because either it's over or already been discovered by the big guys and you will have a hard time competing.
The challenge in capitalizing on trends at the right time is that sometimes they don't pop.