Don't forget that most sellers are padding the cost of shipping to cover Ebay and Paypal fees.
Also, most packages are subject to dimensional weight pricing and not necessarily the weight of the item. If you have an item that weighs 5lbs but is very large and needs to be shipped in say a 24"x24"x24" box then the shipping charges will be more in line with something that weighs 25lbs. Now this is just a guess and I have no idea exactly what the dimensional rates are, but there is a lot more going on than simply adding two things together at times.
I never expect a seller to combine shipping totally, even if their auction states they will do it. I always ask before buying unless I want the items no matter what. Ebay is nothing like it was 10 years ago, the days of really good deals are long over.
