Disputes
If a trade goes wrong while your payment is still in admin, a dispute takes the outcome out of both parties' hands and puts it to an admin.
Raising one
While the payment is held, either party can open a dispute from the order screen with a reason and a description.
The money can no longer be released or cancelled by either side. It waits for a decision.
They read the order chat and the account of what happened from both sides.
The admin either refunds the buyer or releases to the seller, with a written reason shown in the order chat.
Before you dispute
Most problems are quicker to solve in the order chat first. A dispute is for when you and the other party cannot agree.
Outcomes
A refund returns your payment in full and relists the account. A release pays the seller their proceeds. Either way the case and its reason are kept on record.