Let me say again: I am NOT an expert and I am still learning about small business/Etsy/selling on line. These posts are about what I have learned in my first year and the "formula" I came up with for myself personally; and am posting it here in hopes it helps other Etsyans.
There are only 2 kinds of things to discuss here. Things you make yourself, and vintage things over 20 years old.
I do not sell many things I make myself; I have a few, but for the most part if I made it, I keep it or give it away.
So I guess what I have to say about product applies mostly to vintage sellers.
Please - make sure what you're selling is actually vintage. Vintage on Etsy = 20 years old. If it was sold at Wal-Mart last year and looks vintage, that's not vintage.
I cannot stress this enough. Some sellers sell items from the 90's, and legally that is vintage. But for myself personally, I stop at selling things from the 80's. A lot of 80s fashions are trending again, and hot items in vintage markets. While I may not personally wear it, I will sell it.
Secondly: only sell things in good condition. I refuse to buy anything if it is worn out looking, stretched, stained, torn, altered too much, falling apart, etc. Unless it is, say, very old linens with embroidery on them, and then they can be sold as "cutter" pieces for re-fashioners and crafters.
When shopping for inventory, I carefully look over every item for any flaws. Some flaws may be fixed; like a popped seam on a vintage dress. I have used JB Weld to fix several handbag clasps. So some flawed items, I will buy. But not if it's super messed-up.
Dry clean or wash everything. Store things so they don't get sun fading, iky smells, cat hair, etc.
When I list items, I list every single possible thing on it that could remotely be considered a "flaw". If there is a frayed seam, list it. If there is a tiny hole on the sleeve, list it. If there is a discoloration in the lace trim, list it. If the fabric is nubby on the underarm, list it. Take photos of the most visible flaws and include them in the listing.
Yeah, it might cause some people to move on to the next item, but it is way better to loose one or two possible customers than to have someone buy it and then call you dishonest because you didn't disclose all the flaws on the item.
Presentation is everything, I believe. When photographing items, do your best possible job in how things are displayed, hung up, worn, etc.
Try to use natural lighting and show the item in the way it will actually appear.
Take photos of every possible angle. For china, show the bottom. For clothing, show the tag. Show linings of garments. Show the inside of the vase. Everything.
In your description, list every possible helpful measurement. I used to take all garment measurements lying flat; recently I started measuring all around and not expecting the customer guess at the size.
Know something about what you're selling! Know for sure that is it a 1960s wool blend coat with a real mink collar. One of the worst things to do is say it's from one era when a collector with a good eye can tell quite plainly that it is not, in fact. It is as simple as going on line and spending a little while doing some research. Eventually, you'll be able to tell at first glance what era an item is from. Style, fabric, tags, zippers - there are many ways to age an item within at least a decade.
I usually give my items a good 10 year window of possibility unless I can confidently say this if from this particular year. What was made in 1949 is 1940's, but can also be considered to be early 1950s as well. Know what you're talking about.
The deal is not complete till your customer gets their item in the mail and likes what they see.
So when someone orders your vintage dress, wrap it carefully and beautifully. Many seller add a small card of thanks. I add a business card with a message on the back now.
Use as nice packaging as you possibly can. For a long time I used packing materials I recycled from me and my mom both. When I ran out of those materials, I started having to buy new ones. Package items neatly and in the case of china, use over and above what you might initially expect. (I learned about shipping china the hard way.)
When I ship hats I use a big enough box to pack plenty of paper around the hat so it is not crushed.
Your customer is going to be disappointed if they ordered a beautiful hat, beautifully photographed and presented, and they receive it mashed in to a too-small box carelessly taped together and crushed in transit.
I also order cute return address labels for my packages; for the personal touch.
There is so much more on the topics of identifying good vintage; repair, cleaning, storing, etc. There is a book full to say about it, in fact. The best thing to do, if you're a vintage seller or want to get into vintage selling, is buy one of the many books out there on these topics.
I plan on delving into some of it myself in the coming months.
Again - feel free to ask questions and discuss in the comments. Thanks for reading!