Either the robbery is severe enough for the person who was robbed to assemble a little group to catch the robber or they just let it slide. If we know some info about the robber we could let any institutions in the surrounding area know that this person is to be exiled or at least that his missteps be brought up before he is again considered to be part of polite society.
Local neighbourhood watch /militias could also exist and take over some of the polices current work especially when it comes to groups of potentially violent perpetrators.
None of this is going to be particularly effective but it’s not like currently a robbery, or most other crimes are likely to be effectively prosecuted either so I don’t see the big issue.
There are more watertight arguments made by anarchists, syndicalists and the like that you could read and agree or disagree with. But at the end of the day there is little ability for either of us to demonstrate, to me that the police can be fixed with any proposed method, and to you that society without police would work/ be more fair. So ultimately we are not gonna get much further here.
Not in the spirit of the question answer: Land Base impulses on an Easter weekend: sweet dill mustard gravlachs and bread Real answer: Bicycles as many different ones as possible