An SMM panel refill guarantee is a promise to top up, free of charge, any quantity that drops off after delivery, within a defined window. A workable policy defines five terms separately: refill, drop, partial delivery, cancellation and refund. The most important rule is that the guarantee you sell can never exceed the refill window your supplier gives you. Offer 365 days on a provider that refills for 30 and you pay the difference from your own margin. Publish it on the service card, define eligibility rules, and automate the flow.