It depends a lot on how deep the cut is. Often the slice does sort of disappear.
But, I would tell them, that you are going to walk if they don't start cutting better. The slice comes from sloppy butchering practices (duh, Captain Obvious is heeeerre). They make it when removing other parts deemed more desirable.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."