Check your local statutes or consult with an attorney. If you don't have a contract stipulating your authorization to hold the property as collateral, you might actually be violating the law, even if you are owed money by the property's owner. The best thing to do in my opinion is to settle the matter in civil court and get a court order for repayment.

No where did I read that you have some type of written agreement. People often consult attorney's, only to go before a judge and get smacked around. Be careful on this one.

Did this person give you property and you placed cash in their hand?
Are you holding property hostage because this person didn't pay you?
What is the time frame for repayment that everyone agreed upon?
...

No where did I read that you have some type of written agreement. People often consult attorney's, only to go before a judge and get smacked around. Be careful on this one.

Did this person give you property and you placed cash in their hand?
Are you holding property hostage because this person didn't pay you?
What is the time frame for repayment that everyone agreed upon?
Did the person say they would pay as soon as they got it? (I ain't got it).
Have any payment been made? can you provide documented payment?

I'm sure you can see the arguments for each question I have listed above.
Remember the moral high ground doesn't necessarily mean you have the legal ground that may be needed to tip the scales of justice.

The best you could hope for is that in your state the property in question can be legally declared abandoned. If you are communicating with this individual it may be difficult to prove abandonment. The other thing that you might want to consider is filling a suite at your local courthouse for the repayment of the loan. A judge is likely to instruct you to return the property undamaged and order the person to pay.

Even with that judgment it could years before you see one penny, you see, there is another process you must follow through when individuals don't pay court ordered damages. They don't tell you that on T.V. Huh?

A good judge reads deep into the testimony and determines by the preponderance of the evidence that it is more likely than not that you had an agreement and this individual breached the agreement. A good judge does this by listening to testimony. Without a real spec of evidence benefiting you.

GOOD LUCK