Every store gets them. A parcel turns up damaged, the size is wrong, or the buyer simply changes their mind. What you do in the next twenty minutes decides whether the problem costs you a refund or a chargeback, and those two numbers are not close.
When Sello’s partners fulfilled the order, Sello’s fulfillment team issues the refund from their side, per item, with a reason recorded against it. You do not run it yourself from the app. That is deliberate: the money, the supplier cost and the shipping fee all get reconciled in one place instead of being split across two systems that can disagree.
A refund returns the buyer’s money together with the cart fees, apart from the payment processor’s cut. The processor keeps that whether or not the sale sticks. It is worth knowing before you promise anyone a refund down to the last cent, and it is not a Sello quirk. Card processing works that way more or less everywhere.
A chargeback is the buyer asking their bank to reverse the payment instead of asking you. It carries a fee on top of the amount, and the fee stays even when you win the dispute. Someone who gets a quick, polite refund almost never files one, which is the whole argument for refunding fast: the cheap outcome and the kind one are the same outcome.
Open the order in Sello and respond with evidence. Tracking history, the delivery window you published, the messages you exchanged. Disputes are decided on paper by someone who has never seen your store, so the seller with records usually wins. You can also just accept it when the buyer is in the right and the week is better spent elsewhere.
A share of orders goes wrong however careful you are, and pricing on a real margin is what keeps one bad parcel from eating the week. Sello holds a rolling reserve against disputes for the same reason. Returns are a running cost of retail rather than a sign you picked the wrong product.