I guess if people start their path towards medicine with dishonesty, they are likely to continue this pattern throughout their journey. Eventually, it will catch up with them.
On AMCAS, applicants are expected to include contact name for all of their activities (i.e. shadowing). While the odds of a school checking everyone's contacts for all of their activities is probably low, some schools do randomly verify the accuracy of information entered as activities (random audit). Another way to get caught is if you say you worked a 100 hours with Dr. A, who, at one point, also happened to practice with your application reviewing. Said application reviewer is very interested in you as a candidate and decides to call Dr. A, only to find out that you shadowed only 16 hours. This does not end well for the applicant. You'd be surprised by how many people in academic medicine actually know each other in a given multistate region.