Though eBay have recently taken precautions to minimise this occurring, it remains important for prospective buyers to first read the (potentially high) postage costs associated with the auction/Buy It Now item.
It seems some eBayers continue to list their items extremely cheaply, or at least well below their Recommended Retail Price, an advantage underlying the whole notion of eBay to begin with, but then have unreasonably high postage and handling charges. An example could be as follows: you find an item worth $50 in a store for $20 on eBay. The item might be quite small and only cost about $10 to send - yet the seller charges $50 in postage.
Now it is important to note that postal costs, at least here in Australia, are forever rising. It can indeed cost significant amounts to post bulky or heavy items - or include extra services such as tracking or signature-upon-delivery. Obviously international post can be quite expensive. The costs may include packaging, boxing, tape or protective measures (e.g. Bubble Wrap).
But postage should not be a means for sellers to make a profit! Not all sellers are out to get you. In fact, 99% of them are honest, trustworthy people who are just as annoyed about the prospect of a buyer who paid $50 in postage for their (fragile) item to arrive in an envelope with a $1 postage stamp on it which, worse, could be unsecured and/or damaged. This simply sets a bad reputation and results in needless scrutiny from buyers who, quite rightly, want to make sure they are getting a decent deal!
So overall it is just about common sense. It is worth checking where your item is coming from and doing a little bit of research to the postal costs before deciding whether or not it is really worth what you'd be paying. Once you've won an item you're obligated to pay for it.
When performing a search, it is handy to filter your results by "Price + Postage: Lowest(/Highest) First" rather than simply "Price: Lowest First"
Good Luck and Happy Bidding!