[I'll send you one with spent primer, no powder and bullet seated.. ]
Just as a good rule of thumb, a spent primer is not a good indication of a dummy cartridge. A hole drilled into or through the case to verify there is no powder is highly recomended.
About 10 years ago a 1873 Springfield rifle being shown in a youth firearms safety class in Minnesota was discharged into the ceiling. One of the other instructors had a 45-70 cartridge in his collection that had a struck primer, well it was thought to be a dummy because of the firing pin strike.
So no primer or a hole through the case is the only way we are allowed to bring ammo displays into a class.
And as Pahoo says,
For the message of the Cross is foolishness to those who are perishing, But to us who are being saved, It Is The Power Of God. 1Corinthians 1-18