I'm quite sure that most eBay sellers are also buyers (and vice versa). Whichever side we are on, the fundamenatal premise of eBay relies on successfully moving items from seller to buyer. Usually this is a physical item.
I am also quite sure that most people have experienced the problem of not being at home when delivery of the goods has been attempted. This results in trips to the Post Office (shops or depots) & Parcel Depots or the hassle of contacting the courier to rearrange a delivery slot. It's at this point that all the benfits of shopping on eBay and other forms of home shopping, start to rapidly diminish.
There are products out there that effectively mean that you can always be in, even when you're out! They range from advanced hi-tech reception boxes, through more simple, but effective, one-time use boxes and even to a key storage box with a code management service that releases a garage/shed/conservatory key to the delivery driver so that he can safely leave the parcel until you get home.
Rather than try and describe the options here, I would recommend taking a look at a trade journal on this topic called "fulfilment & e-logistics" at what they call "unattended delivery solutions". You may find something suitable for either yourself or some particular customers of yours. I don't work for this journal, but I have been testing a solution to this problem.
Not wanting to get too overtly commercial I won't directly say which option is mine; suffice to say that the key to getting the delivery completed first time could be a perfect Neighbour In a Box .