I have successfully sold quite a few things on ebay, but have bought very little. My recent Gucci scarf transaction went like clockwork and I'm very pleased with it.
My rules are: only buy from individuals; never buy from anyone selling in bulk; look to see their feedback for buying as well as selling; never buy from abroad; ask a lot of questions.
When selling give clear descriptions, brutal honesty about the condition, measure everything and only give refunds if the item is not as described. I had one return when I washed an Issey Miyake skirt which had a small mark, and assumed it had come out in the wash and didn't check before I sent it. It hadn't. Also if you really don't want to let something go for .99p, put a minimum price on it.
Do share your own experiences.