First, before ever listing something for sale, it is critical to have a good sense of what it will cost to ship, and have that covered in the price structure somehow. Before offering "free shipping," check your item out using a scale. The one I use every day came from a thrift store for $20. I see them pretty often. It is easiest to just use the ebay shipping calculator, by entering the external dimensions of the box, the final weight of the box, and the shipping method. Then it's probably a good idea to add a handling charge. Ebay charges a fee on shipping (10% if you have no store), and PayPal charges 2.9%, and packing supplies are not usually free. On high shipping costs, that 12.9% becomes pretty significant.
As to how to ship things with high shipping costs, it can be a struggle. Eventually you will get some sense of what shipping various things costs, but there is always some uncertainty due to when "Dimensional Weight" takes over, and where, relative to yourself, your item is going. I steer clear of big items unless I find something worth enough to make it worthwhile to buy and sell. Customers will have a sense of what they're willing to have into something, and I generally have to figure out what that is, and back out the shipping cost, to set the price. If that doesn't leave me enough money for the work involved, I won't buy that item for resale. Big and/or heavy items typically need to be packaged really well to protect them during shipment, and that tends to make the boxes bigger than you might first imagine, and a lot of work.In general, try to deal in small items that fit in boxes less than one cubic foot. It's a whole lot easier.
