Given the upredictable prices of Robertsons badges what is the best strategy for realising the best price?

In short nobody really knows but as long as you get a fair and honest price that you are happy with then who cares.  The best policy is to monitor the market and judge the average price per badge.  Remember sometimes a badge may go for double or even treble it's usual price if two Ebayers want to fight it out but then there is also the unxplainable time when auctions go for the maiden bid of 1p and the seller is left licking their wounds.  If you value a badge then use a reserve but remember if you set it high then you may get no bids at all and wind up with just your Ebay fees to pay out.

If your thinking of covering your Ex's by high postage this doesn't work either as these auctions almost never get a bid but you still get charged your insertion fee.