Displays and testers
Display products and testers are counted apart from stock for sale.

Why it matters
A tester, a display product, a sample: they’re on the shelf, they have a barcode, but they will never be sold. Counted with saleable stock when they aren’t in it, they create a positive shrinkage that doesn’t exist. Recorded in stock then missed at the count, they create the opposite. Either way, your stock is no longer accurate.
What often happens
The tester scanned by mistake. It has the same code as the item for sale: the counter can’t tell the difference.
The moved display. A display product put back on the shelf with the others, or the other way round.
No common rule. One store counts them, the other doesn’t: results can no longer be compared.
What to do
Mark them. A “not for sale” label or a dedicated tray.
Set them apart. Outside the counting zones, or in a zone of their own, counted separately.
Set a single rule. Decide whether they are in your book stock, and apply the same rule in all your stores.