The sellers usually finalize a trade as soon as they see your payment, which can sometimes take an hour or two. If you've paid but are still waiting there is nothing to worry about, for all online trades are protected by the arbitration bond and the seller cannot run away without losing the bond. If there are any issues with a trade and the seller won't finalize it, you can dispute the trade to have LocalMonero support resolve it. If you are buying or selling Monero online, you can dispute the trade after you have marked the payment completed. A dispute can no longer be started if the trade has been finalized or if it's a local trade without arbitration bond protection enabled. When a trade you're involved in becomes disputed, you'll receive an email. A disputed trade is usually resolved within 24-48 hours.