The other responders spell it out pretty well, the cost of mailing envelopes, sealing tape, etc. I would add one other item -- $2.00+ a gallon gas. You have to figure that in too, especially for someone that sells a lot on ebay. Those trips to the post office eat up a lot of expensive gas. I have also had a few sellers go to some length to explain to me [after complaining to them] that they charge for their time as well, the time it takes to list the items, print packing slips, get the packages ready -- I do not do that, but a few sellers do.
All that said, I still check out the shipping charges before I bid -- that is always a smart thing to do. And if it is a chip you want really bad, you pay the shipping charge, if it isn't too outrageous. Not to forget, the post office and UPS continually raise rates. Everything goes up. And most of the time, it is still cheaper than a trip to the location to get the chip yourself *smile*