Finalisation ratio is the number of orders that closed cleanly (both buyer and vendor signed the release without a dispute) divided by all completed orders. This reading covers what the number tells you as a buyer.
Above 95 percent
Healthy. This is where working vendors sit. Ninety-five out of a hundred orders close without any moderator intervention. Buyers were satisfied enough to sign the release. Vendors delivered what they promised.
90 to 95 percent
Slightly elevated but not necessarily bad. A vendor with a high volume of orders and a moderate rate of small disputes can sit here without any single failure being severe. Read the dispute record to see whether the disputes were minor (small refunds, missing items in a package) or major (undelivered orders, wrong products).
Below 90 percent
One in ten orders required a moderator to arbitrate. This is a warning sign. Something is happening that is not being resolved between the parties. Read the recent reviews and the dispute pattern before ordering.
What the number does not measure
Whether the vendor won the disputes they had. A vendor with 90 percent finalisation could be a vendor where 10 percent of orders had a dispute but the moderator ruled in favour of the vendor every time. This is not visible in the ratio alone.
Read alongside dispute ratio
The two numbers together tell the story. High dispute ratio (say 8 percent) plus high finalisation (95 percent) means many disputes but they mostly get resolved in the vendor's favour. Might be a vendor whose customers are unreasonable, or a vendor gaming the system. Read the reviews to work out which.