My only words of advice as a regular seller on ebay is:
BE REALISTIC ABOUT YOUR POSTAGE CHARGES AND DON'T BID ON SOMETHING THAT IS OVERCHARGED!
The whole postage thing on ebay is getting out of hand. This morning I posted several gamecube games at a cost of 60p each. My charge on ebay was £1, the difference going towards envelopes and reciept paper. I have just been looking around for films and dvds that are exactly the same size/weight as what I posted earlier and people are charging £6! £6? I would expect next hour delivery by 3 young Brazilian beauties for £6! Neadless to say these items had minimal bids, which is good and more realistic charges of £2.5-£3 were having great success.
Airmail is also not as expensive as you may think. When selling on ebay always allow bids from the EU as the postage costs are very low. At the moment EU countries are going mad for your old mobile phones. In the past weeks I sold a Nokia 6320 to a guy in Poland for £67 and a Sony Ericcson to a French bidder for £97! Postage costs: Poland £3.19, France £3.48. Admittedly I charged slightly more than this because only selective Post Offices do airmail service and the packaging has to be better, but without allowing these guys to bid I would have no doubt not acheived such a high winning bid.
Use the Royal Mail website and the scales from your kitchen/bathroom to judge a decent postage price. Consider on smaller items a free delivery charge and make sure you write this in your title. Don't be frightened when bidding on a best offer or buy it now price to enquire about cheaper postage and DO leave poor feedback for people who charge first class and insured but deliver parcel force and signed for. These are not the same thing.
Any comments welcome