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DMcDHonus Wagner by Dennis DeValeria & Jeanne Burke DeValeria, University of Pittsburgh Press, 1998
A solid, well-written biography.
Honus Wagner On His Life and Baseball, William Cobb (editor), Sports Media Group, 2006
A compilation of autobiographical articles syndicated in American papers in the 1920's. The editor takes pains to explain that the articles were not ghostwritten but were authored by Wagner himself. Have only browsed the book but it looks like it will be a fun read.
Anything is possible if you don't know what you are talking about.