It would be impossible to work out the combined postage in advance on unknown items. How do you know what items someone will buy before they buy them?. I have to work it out after they have finished shopping. Sometimes it surprises me how heavy the box or packet will get with the extra items and packing. Making sellers put combined postage may be ok for sellers selling only 1 or 2 types of items, but for those of us selling hundreds of different things, it just wouldn't work.