A few weeks ago I bought 50 of the same item from China. They cost around £6 each, and I managed to sell them (using Adwords, and not on ebay) for £19.99 each plus postage.
I took the profit and bought 120 more. A lot of competition has sprung up in the weeks between then and now, so I sold these at £17.99 - again, without having to go via ebay. I have 3 left. Because I was buying more, I got them at about £5.50 a piece. I also charged £3 postage per item, and made about 20p after actual postage and packing material costs.
So, from my initial outlay of £300, I have made - according to my shopping cart software - £3609 in under a month. Delighted? Me? You betcha.
I think the market is starting to get flooded - the item in question is now down to about £9.99 with free postage on ebay - so I don't think I'll get any more. Great while it lasted, though, and it has shown me that ebay isn't everything, and that not everyone uses it.