A quick search on Ancestry.com shows that this winner could have been Frank Joseph Zak, who would have been 42 at the time of the contest. I found records showing he was born in August 1881 in Pittsburgh, PA. In the 1900 census, he was living in Allegheny City with his mother Leopoldina and sister Mary.
In 1917, Frank worked as a funeral supplier manager on 7th and Liberty. By 1942, he was employed by a florist on E. Ohio Street and was living on the North Side of Pittsburgh with his wife. There's a lot more information I should be able to find about him, but this gives you an idea of the usual pieces we stitch together about our relatives: dates, locations, occupations, etc.
While all of these facts are extremely important, there's just something great about learning he won a car decorating contest. It shows us more about Frank as a person: his personality, his fun side.
Wouldn't it be wonderful to find more about your ancestor from an item offered for sale on eBay? I haven't been that lucky, but maybe you will!