Police in Seattle held a gun buyback drive several years ago that didn't go exactly as planned.

In 2013, they offered gift cards for unwanted guns but, people interested in buying guns at low prices showed up offering sellers cash. At one point, the cops ran out of gift cards and began offering people IOU's which prompted many sellers to go to the private buyers who had money.

Police officers in Seattle, Washington held their first gun buyback program in 20 years this weekend, underneath interstate 5, and soon found that private gun collectors were working the large crowd as little makeshift gun shows began dotting the parking lot and sidewalks. Some even had “cash for guns” signs prominently displayed. - dcxposed.com

One website, econlib.org, reported that "Police stood in awe as gun enthusiasts and collectors waved wads of cash for the guns being held by those standing in line for the buyback program".

Free enterprise is alive and well in Seattle.