A false accepted report may be attributed to a respected scholar without a reliable source. A false concession may exaggerate what the opponent actually granted.
Example 1: “A certain expert said this,” without verifiable attribution; the report must be checked.
Example 2: an opponent concedes “some examples are valid,” but the concession is restated as “all examples are valid.” That changes the conceded proposition.
In each case the argument borrows the appearance of a warrant it has not established.