I have done alot of Ebay selling. Here are some tips I would give. Make sure you know the weight of the product you are mailing. Postage costs can eat you alivewith selling on ebay, if you are not accurate. You don't need to buy a lot of boxes for ebay selling. The post office has envelopes and about 3 common sizes of flat rate boxes for free. Also always make sure you pay for delivery confirmation. I had one buyer who said they never received the product I shipped. How do you really know if they are telling the truth? If you don't return the money they will leave really negative feedback which will affect your future ebay selling. Concerning mailing again, you might want to consider only selling light items which don't cost much to send such as jewelry. If you are ebay selling through a wholesale distributor and they are taking care of the dropshipping, make sure they have a good supply of products available for shipping and they are not telling you a story. The items could be back ordered and the wholesaler tells you that they are available for shipping right now. Big trouble when the buyer doesn't receive their product for several weeks and you thought it had already been shipped and received.
One real tricky scam when ebay selling is the international customer who wants to pay more than you are advertising for or more than the top bid and they want to pay by Western Union. It is a scam. Western Union does not do Ebay Payments. Fake checks which look very real can also be sent to you, particularly with the above scenerio of paying more than the the auction is posting. Be a smart with your Ebay selling.