Maybe the example would help to describe the expression I am looking for:
Say - a sub-par school or organization makes a promotional video, whereby they make the school look way better than it really is. They accomplished this by interviewing a few successful students, showing only the best parts of the school/classes, picking a few angles, and omitting 80% of what really represents the true situation.
I have heard the following expression, but not sure whether it's appropriate, or even phrased correctly:
Turn chicken into a chicken soup.
EDIT: actually the expression was
Make chicken salad out of chicken $#!%"
coined by Brock Lesnar. Obviously it's less befitting than others mentioned on the thread.