When bidding on eBay, it is always worth knowing the value of what you are bidding on.
Make sure that you research the cost of items that you are interested in.
I am always amazed at the number of auction items I am watching or bidding on where people actually end up paying more than what the item retails for. Sometimes, sellers even have a starting price of more than the RRP. And once you add on postage costs, items are often being sold for substantially more than the item's retail price.
So, remember, always ensure that you know the RRP of the item you are attempting to buy.