I have been selling on ebay for a few years, only in small quantities and as a hobby, but I thought I knew quite a lot. Having read this book I realised I knew nothing. For example simple things such as whether your item title will show up in a buyers search, is it misspelt, have you left out vital information. Stuff that's really obvious when you think about it, but I hadn't been. It's also meant that I have profited from other's mistakes, buying items that have been badly marketed for a much cheaper price! My sales have definitely improved and I've streamlined how I work. The one thing he doesn't tell me, is where I can find cheap stock!
Since reading Dan's book I've spent a lot more time looking around ebay, getting ideas on what works, checking out what's selling well and considering how I might open a shop when I have more time.