 The sister of the real Butch Cassidy often visited the set, and her  presence was welcome to the cast and crew. During lulls in shooting  she would tell stories about her famous brothers escapades, and was  amazed at how accurately the script and Newman portrayed him. Before  the film was released, the studio found out about Butchs sisters  visits to the set and tried to convince her to endorse the movie in  a series of ads to be shown in theatres across the country. She said  that she would, but only if she saw the film first and truly stood  behind it. The studio refused, saying that allowing her to see the  film before its release could harm its reputation. Finally, at  Redfords suggestion, Butchs sister agreed to do the endorsements