THIS IS VERY IMPORTANT – the #1 reason for dissatisfied customers is simply that they have misunderstood cropping.  

Pro photos – particularly those published in newspapers – are sometimes cropped for a specific space that is not suited for standard print sizes. For instance, suppose you want to print a square image on the popular 4" by 6" photo paper: if the square photo fills up the photo paper space, then the customer will not see the top and bottom inch of the photo. To see the whole photo, the customer must order the photo "uncropped," which, in this case, would put the square image in the middle of the 4x6 print with an inch of white space on either side. 

Most people want to receive the entire photo, so we suggest that you encourage customers to ALWAYS order their photos uncropped.