At the start when Bert is saying goodbye to Al the is a blue and white awning visible in close ups that disappears in wide shots.
This episode seems to be the weakest in terms of likely scenarios: it's highly unlikely the police would mistake a zero crime-detection rate for a zero crime rate and even more unlikely they would think that PC Penhale's mere presence had eliminated crime and that ability would transfer to a bigger town. It is also unlikely that the school children, having seen what would happen to their favourite toys, would then bring those toys in the next day. And it is unlikely that a tenant would be able to authorise work on a house, and Bert should know that.