I'll try not to sound too preachy in answering your question!
Any idiot can stand on the corner of the street and sell a £10 note for £9. It takes patience, hard work, curiosity, setbacks, worry, investment, friends, favors and more besides to sell a £10 note for £11. Fortunately most people do not possess these qualities - or at least are happy to just sell on price.
Price is only 1 of the 7 marketing 'P's' the others being Product, Place, Promotion, People, Process and Physical evidence. Have a look at the websites of Harrods, Fortnum & Mason, John Lewis, Waitrose etc. and I'll bet you'll see plenty of items that are so called 'commodities' yet they sell them online anyway.
The trick to charging more and being successful is to give people reasons to use you. It may be how your eBay listing template looks, your returns policy, your feedback, how you package & send your goods out, what your invoices looks like (most competitors I've seen are rubbish), how your listing photos look to customers, how quick you respond to customers when they ask you a question etc, etc. All this adds up and means that you can justify the 'value gap'. What I mean by that is the price difference between you and your competitor. If you have not created enough perceived value then you won't be able to justify charging more.
I've been in field sales for nearly 20 years and have sold everything from Yellow Pages advertising to industrial electronics. If I had £5 for every time a potential customer said to me "it's all about price these days mate" I'd be a rich bloke. Things in life are rarely black and white, more often they are shades of grey. Very, very few people make purchasing decisions only on price and price alone. They might say they do, they might even think they do but they don't.
I'm not saying you don't have to be competitive and I'm not saying that commodities don't exist what I'm saying is that in order to sell anything you have to look at the overall value you are offering as a business to your customers.
Remember there is only 1 of you and that is something nobody else can copy!