Advice re checking whether bikes are stolen or not

I am not a lawyer - nothing I write should be considered as anything other than speculation. You should consider advice from a qualified expert.

Apologies if you've already considered all of these:

Your liability here could be both criminal and civil - Knowingly handling stolen goods could get you in a heap of shit with old bill, and recipients of the bikes could hold you responsible for anything that happened as a direct result of the bikes being stolen.

Performing some level of due diligence on the provenance bicycle that you receive may mitigate these risks, and a transparent policy and process can protect your organisation from being accused of any shady business, or from the impact of any shady business.

That process might include (among other things)

• Communicating with local police forces to cross-check bikes against known stolen bikes,
  
• Having a cooling off period of a few months between receiving a bike and passing it on
  
• Only receiving bikes from vetted sources
  
• A process for handling bikes identified as stolen (such as taking reasonable steps to find the owner, including informing the police)
  
  

Ultimately, the test would be one of reasonableness - i) Have you taken reasonable steps to ensure that the bicycles are not stolen, and ii) have you taken reasonable steps to ensure that your steps are reasonable.

I'd argue that i) can be a relatively simple framework, and that ii) is as easy as informing your local police force of how you intend to implement, and obtaining legal counsel's opinion.