If they don't have receipts for the valuable items, unless they paid for them by cash, there should be a transaction on their bank account.
If they say it was cash, where did that come from?
What you need to think is, if you were in the same position with no receipts, how would you prove you owned the items and what age they were?
If the expensive items were in the same area, is that likely or is it inherently improbable?
Do their versions of events stand up, are they consistent? If there are various folk involved, do their accounts match up?
I hope you're getting the message not to accept everything at face-value and you must take time to do some research.