[goonergaz]

They are worth what someone is prepared to pay and you sell.

Example, I have an item and I don't want to sell it for less than £100 - however the market only wants to pay £80...the value to the market is lower than the value to me, so I won't sell.

I do this on eBay, ask a high buy it now price and have 'open to offers'. I set the 'accept' level to the lowest I would accept without thinking and the 'reject' to lowest I would reject without thinking...anything else is negotiable...but in this area you can also explain the worth to the potential seller.

So in the example above;

BIN = £120
Accept = £100
Reject = £80

Anyone bidding above £80 is worth speaking to and maybe you can say 'never seen this condition before' etc.

Long story short, advertise for more than you want and listen to reasonable offers.