How did the Ginyu force not know about concealing power levels?
The ability to freely concentrate, suppress, and raise your ki is actually a pretty rare power. None of the villains on namek other than Frieza and Captain Ginyu had the ability, for instance.
All of the Z fighters learned it from Kami, I believe.
Basically, most characters can't magnify or suppress their power, only redirect and reshape it. Seems like the warrior namekians have a natural gift for it, though