Co-mingled inventory means Amazon uses your product's UPC to fulfill orders from any seller's identical inventory — not specifically your units. This eliminates the FNSKU stickering step and reduces prep cost.
The risk of co-mingling is receiving a return or chargeback tied to a different seller's units. If another seller on the same listing ships counterfeit or damaged goods, your account can take the hit.
Stickered inventory assigns each unit an FNSKU tied to your seller account. This costs more at the prep stage — labeling is an extra step — but gives you full traceability and protection from co-mingling risk.
For private label products where you are the only seller, co-mingling is lower risk. For products on competitive listings with many sellers, stickered inventory is the right choice.