Very specifically, the setting is that of Spider-Man: Homecoming, and the character in question is Adrian Toomes/the Vulture.
For those not familiar with the MCU, there was an alien invasion several years ago, leaving behind a lot of alien technology. Toomes - at the time a perfectly legitimate contractor of some kind - had a contract with the city to salvage it, and had invested tremendously in doing so, only for a government agency to swoop in and take over all of it at the last minute. He illicitly retained some of that alien tech, developed weapons and other criminal devices out it, and started selling it. He set up a business of doing this (built on/by robbing that government agency of alien salvage, mostly without them noticing, since they merely lock up said salvage after documenting it an storing it, opting not to use it for themselves).
He doesn't seem to have (necessarily) become a millionaire over this, but he is wealthy enough to afford a classic car and a large house in uptown/suburban Queens, New York.
I'm writing an AU where he was not caught and imprisoned at the end of the movie. Among other things, I am trying to figure out a way for him to have laundered this illegal arms dealing money. All I can really think of us is that he maintained his salvage company on the surface (and that he may have even continued working salvage, sometimes), since money-laundering usually works best through "service" companies. But that feels shaky and incomplete, and I just don't know enough about money laundering to figure out if this is even a feasible way of doing so, or how it would work even if this were a good idea.
Any and all help would be greatly appreciated! ♥