Save yourself time and money and invest in a postal scale. When putting items up on eBay, I found that it was much more efficient if I packed them first so that I could provide accurate shipping measurements and weight. This allows you to set up calculated shipping so that no matter who buys, they will see the correct shipping price for their region. To do this, take photos of your item, then wrap it up securely and box it. I usually leave it unsealed until it sells so that I can slip in an invoice before I ship it. At this point, you can measure the box and weigh it on your postal scale. Input the dimensions and the weight into eBay when you’re creating your listing and you’re good to go.
After the listing is created, I usually add the last 5 digits of the auction id and a name so that I don’t forget what’s in the box. Now, when the item sells, you don’t have to worry about boxing it up. You can just grab it off the shelf, stick a printed message/invoice in it, seal it up, and send it on its way. Personally, I like to add a note to the box that thanks the customer for their purchase and politely asks them to contact me if there are any issues before leaving feedback. In addition, if everything is good, I ask for a 5 star review.
This postal scale is the best one I have used in this price range, and over 500 5-star reviews can’t be wrong! In addition to this postal scale, I also recommend that you get a Zebra 2844 thermal label printer.