An undercover police operation didn't work, because Canadians were being too nice. 

Earlier this year in Vancouver, Canada, there were some horrifying instances of disabled people in wheelchairs getting beaten up and mugged. To catch the criminals, the Vancouver Police Department hatched a plan. The Ottawa Citizen described the idea:

Working with other VPD members, peer support workers and rehabilitation specialists, [Vancouver Police staff sergeant Mark] Horsley hatched a cunning scheme. He borrowed a $16,000 electric-powered wheelchair, grew some facial hair and wheeled into the DTES, undercover.

Hosley, equipped with a wheelchair and disguise, tried to "bait criminals by flashing cash and valuables, such as cellphones and cameras." 

Sources: Ottawa Citizen