When I hear about someone that comes up with a garage "invention" that will "save the world" while being very "inexpensive" and/or "easy to install" or "inject" (whatever) that a simple rule of thumb might be:
Most Likely Real: They can get their own financing easily enough while keeping it secret until they are ready to sell it to the world.
Most Likely Real: They will just publish the instructions and let the world have it.
Then if they are for real, there will be $$ coming their way for future ventures or even just speaking gigs.
Most Likely NOT Real: They want to get a "distributorship" or "dealership" network setup (read: $$$$$$).
Most Likely NOT Real: Nobody else can figure out the "invention" based on a sketchy amount of information.
Most Likely NOT Real: When fantastic claims are made w/o ANY good evidence citing some "conspiracy" that makes them keep quiet.
MIGHT Be Real: Using some alien technology that we just cannot understand yet, but the best scientists have free access to it.
Anyway...