There have been a couple of times when a muggled geocoin has appeared
for sale on ebay. This has then been advised on the forums and at that
point things seem to go wrong as the seller receives emails from
numerous people and no one seems to know what to do and how to proceed.

By virtue of my ex job and liaising with someone with current
experience we came up with a method of dealing with missing coins.

When a coin goes missing from a cache make a note of the cacheīs

Then should the coin appear for sale on ebay or similar sites you
should contact the seller to establish the details of the coin and
confirm that it is the stolen one, then approach your local police to
report a stolen coin.

After the initial approach to the seller no further correspondence
should be entered into and no thread opened on the forums. This will
prevent the seller receiving large numbers of emails and make them
back away and dispose of the item.
The police will be able to take the report and issue a crime report
number. They will need to forward the report to the force who cover
the location where the coin was stolen, hence knowing where it went from.
At the same time you should advise them that you have identified the
missing coin as being for sale on ebay and give the sellers details
and the item for sale details.

They should then be able to approach ebay etc and investigate the coin
as they have recognised methods for corresponding with the site.

Hopefully they may then be able to get the coin returned to the
rightful owner but there is far from any guarantees.
The likelihood of any conviction for the removal of the coin is
negligible and isnīt the purpose of this exercise, all this does is
increase the chance to get the coin returned with the minimum of fuss
and without alerting the seller or bombarding them with emails.

I hope this makes it easier in the future to resolve these matters.

In order to keep this thread clear I've pinned and locked it, if you wish to discuss it and related issues please feel free to open a new thread.