How much and how hard should an umpire be shaking the bat while checking for wobbles and rattles?

CHECKING FOR WOBBLES IS TOUGH TO TEACH BUT WHAT YOU ARE LOOKING FOR IS A BAT WHERE THE CONNECTION IS COMPROMISED.
AS YOU WAGGLE THE BAT (WRIST FLIP FORWARD AWAY FROM THE BODY AND THEN BACK TOWARD THE BODY), THERE IS A TIME LAG FOR THE BARREL TO CATCH UP WITH THE HANDLE.
IT CAN CERTAINLY BE DONE WITH JUST ONE HAND MIDWAY UP THE GRIP.
How exactly can umpires determine if a mark on the barrel of the bat is just a scratch of the paint versus a crack that appears to have affected the actual barrel?

COMPOSITE BATS ARE NOW DESIGNED TO BREAK FROM THE INSIDE OUT AND PAINT SCRATCHES ARE FROM THE OUTSIDE IN.
SO FOR SCRATECHES LOOK TO SEE IF THE EDGES ARE EXPLODING OR IMPLODING.
SCRATCHES ARE USUALLY SEEN AS SINGULAR AND ALONE
CRACKS OFTEN (BUT NOT ALWAYS) SPIDERS OR RADIATES AND ARE MORE A GROUP OF MARKS THAN A SINGLE MARK.