FIRST never, ever use an already used box (with one exception, I'll get to in a minute). That is just tacky. Yes, boxes are expensive BUT if it means a great first impression, it's worth it. I used to buy mine from U-Line but the postage is outrageous and you have to buy in lot quantities. THEN you have to store them. If you search for "mailing boxes" on google you will find many places which sell smaller lots. Some Staples stores carry various size boxes IN the store as do some WalMarts -- so you can buy one or two at a time and not have to pay postage.
However, the BEST and SAFEST way to ship is to use priority flat rate boxes if the items you sell weigh more than 13 ounces. First, after you reach 13 ounces, you HAVE to go either priority OR you have to be selling a book and send it book rate which takes forever and the handling of book rate is pitiful. Priority boxes and envelopes are FREE. Go to usps.com, open an account, and you can get all different size priority boxes and envelopes FREE and there is no shipping charge either. I use flat rate boxes for the antique medical books I sell, and my buyers have NO qualms about paying $11.70 to have their book shipped in that manner. Anyone who knows the value of the item they are buying, would be SICK if it were to arrive damaged, is more than willing to pay to get it in perfect condition. Other items which are large and heavy HAVE to go priority -- and flat rate is the best. Large, flat rate boxes ship for right around $18.00, medium for $11.70. Flat rate means it mails for the size of the box, regardless of the weight.
NOW why am I so "big" on priority? Because the people at my post office taught me long ago "do not EVER EVER EVER mail anything breakable or that would damage easily ANY way but priority". Priority mail is HAND sorted. It is not thrown into the carrier where all first class and other class mail goes. No heavy box is going to land on top of it. When priority is moved to the truck for shipment to the sorting center, it is put in the truck LAST and taken out FIRST and kept apart from other mail. It is never thrown onto a conveyor belt. A 200 pound tire doesn't land on top of it. THAT is what happens to first class, book rate, and any other rate of shipping. Packages are DUMPED onto conveyor belts; priority mail is not.
Now back to regular boxes. I buy on line a lot. If I receive a box that has three shipping labels on it with the newest one attached over the last two, and marks and scribbles all over the package, it's a big turn off. I feel like the seller doesn't care about me or the item I purchased. After one trip through the mail most boxes show wear and tear to some degree. Then add another mailing label, more tape, and they get to looking really pitiful. The ONLY exception I make are Amazon boxes. They are sturdy. They usually come in looking brand new. NOW you have to peel off that black tape they put on them and take a felt tipped black pen and NEATLY black out any pre-printed numbers Amazon has on their boxes -- BUT I have found they look VERY neat and clean if carefully repurposed.
Another thing --- bubble wrap is expensive. BUT so is losing an item. If it's insured, sure it's not going to cost you out of your pocket ... but I'm willing to bet the buyer will NOT be back to visit your shop. If selling something breakable, your box should be twice the size of the item you are shipping. The item should be wrapped and double and sometimes triple wrapped in bubble wrap with STILL enough room under, around and on top of it to put MORE bubble wrap. Don't use paper -- it's heavy. Usually those inflatable bags are too large and send you to yet a larger size box. Peanuts cost a fortune. I put my breakables in bubble wrap. I put bubble wrap under and around and on top of them. THEN I use a newspaper and put ONE layer of wadded up newspaper on the sides to firm up the box. THEN put the name and address of the person you are sending it to INTO the package, along with your return address just in case the post office outsmarts you and destroys the package --- that information can still get it to the recipient. Have good, heavy wide wrapping tape. Wrap it around the boxes at least twice both ways. THEN using the same wide packaging tape, TAPE THE SIDES OF YOUR SHIPPING LABEL DOWN.
AND for shipping in envelopes, never, ever just slip something into the envelope. Again, bubble wrap it -- use backing boards and plastic bags for things that may bend .. and don't use Zip Lock bags -- again TACKY.
Two years ago I ordered some socks for our grandson for Christmas. They arrived in a metallic bright colored, heavy "envelope". Inside each pair was in plastic wrap. The name of the company was in each package and attached to each package was a business card. Last year I bought from the same company -- yes their product was wonderful --- but it was the PACKAGING that got my attention!!!
I hope this gives everyone who reads it at least ONE new idea. AND I'd love to have you share some of YOUR ideas with me! Ann