Readers over the sales floor and the stockroom, standard practice. Bleed rarely spans the whole wall; it concentrates where construction is thin. Back-room stock racked against that section reads through the wall, and the floor count inflates without a single item moving. Toggle the shielding.
The racks hold 14 items; 6 have sold, yet the count reads 12 of 14: 4 back-room items behind a thin wall section register as sales-floor stock, keeping the number above the restock trigger. Customers only buy what’s in front of their face; most won’t ask what’s in the back, they just leave. Paint the wall and every item counts where it actually sits.
On your floor we prove it the same way: reference tags on both sides of the boundary, controlled read testing before painting, and the identical test after.