The last time a major test was conducted of airport TSA screeners in live, real world conditions, fully 90+% of simulated guns, bombs, and knives made it past their personnel and screening devices undetected and unchallenged.  I wouldn't expect results using hired rent-a-cops or slumming college students to be a whole lot better.

Speaking to personal experience, the last time I walked through security at the Prince Kuhio Federal Building, I happened to be wearing my full-size Applegate-Fairbairn Combat Folding Knife.  I wasn't challenged.  If you Google this knife you'll learn that it's no petite or easily overlooked toy (the darn thing weighs almost a half pound).  So why was it missed?  Maybe the screeners were overworked, underpaid, or both.  Can a purely civilian venue buy better security?  It's doubtful.