When your considering bidding on an item but your unsure what the item is actually worth try a couple of these tips.
Firstly, search for the item by either cutting and pasting the item description in the search bar. All current items with number of bids and current totals will be displayed.
Now click on the completed listings and you'll see all previous winning bids for that same item. If your in the ball park for a good deal then bid away.
Another tip is to widen your search so its not so specific, do a completed listings search on those items and you should have a good idea on what a reasonable price to pay really is.
If you want to be a bit more inventive , especially with new items, do a general search on the net to get the actual retail costs of the item, allow for postage and handling costs and if your still under then bid away.
Finally, check the feedback scores of the seller, They may have just bought the item thats up for sale and it may appear hyperlinked in item number from previous sellers.