Quality is the standard of something as measured against other things of a similar kind; the degree of excellence of something. In clothing, quality is defined by materials and craftsmanship, no matter the type of item. This means the durability and expense of the material, the patterning and finishing, hardware and decorative items, the quality of the label itself and what information it contains. These principals apply to both vintage and new clothing. However, when buying new, remember that there are additional human rights, environmental and ethical aspects to consider.
Learning about clothing construction will help you spot Grey Market gems that you'll want to keep around. It will also assist you in purchasing new clothing wisely. Remember, the name of the game is shopping from the highest quality sources possible and getting the most wear out of each piece of clothing you own. Once your knowledge extends beyond the basics, you will discover the thought and care that a great garment requires. There is a creative magic contained inside every great designer and a lifetime of skill in every pattern maker and sewer.
The textile is usually the most expensive part of the production, so if it's of good quality, usually the rest of the details will match. The easiest way to tell what fabric you are dealing with is to look on the care label - it should give you fiber percentages (ex: 75% cotton, 25% linen). This is also going to clue you in to how you should be storing and caring for this piece of clothing. The best part about shopping in person is being able to feel the 'hand' of the fabric - what does it feel like? Some will feel better, fit better and wear better than others. Make sure whatever you choose, you are willing to care for (ex: dry clean only, hand washing, air drying, conditioning).
The most sustainable fabrics are those made from plant sources. Examples of natural fibers are hemp, cotton, linen and bamboo. Natural sources are best because they can worn well for years, they biodegrade over a reasonable amount of time, and they come from sustainable sources (if properly managed). However, just because a garment is natural, doesn't mean it's good for the earth. Rainforests are slashed to grow garment crops, millions of cubic litres of water are used, shipping and packaging create more waste, and most of our garments end up in landfill. Natural is better overall, but buying secondhand still beats buying new any day of the week. Look for 100% natural (not blended with synthetics) and organic when possible. These are going to be more casual items like t-shirts, jeans, summer wear (functional items with breathability).
Another category of 'natural' textiles comes from animals. Most animal-based textiles will last a lifetime if it cared for properly (conditioning leather + fur, hand washing silk and wool, proper storage). The modern capture of animal resources is extremely problematic and wasteful. However, it is important to note that many of these items are of superior quality, so buying secondhand can be a great investment. The damage has already been done, we should make the most out of what we already have. This category includes all types of leather and exotics, fur, silk and wool.
Synthetics (polyester, faux fur, faux leather, elastic) are petroleum-based. They take hundreds of years to degrade in landfills, creating the same problems as regular plastic use. These are also the same fabrics that throw off microfibers into our water system through washing. This category includes most athletic and leisure wear, as well as a lot of undergarments. If you are going to wear artificial fabrics, use a microfiber collector when washing (guppy bag, cora ball, etc) and air dry to keep these in use longer (the heat of a dryer will destroy the elastic properties of lyric, spandex, etc).
Link to more info about different fabric types.
cut + stitching
The cut of a garment refers to the shape of the pieces that were patterned out of. A high quality cut will sit differently on the body, giving structure or shape and fitting beautifully. Any garment can be altered to fit, however you want to start with a piece that already has great bones. Look for interesting seams and sewing techniques. With jackets, a full lining is a tell-tale because more time and material were used in the finishing.
One of the basics is that clothing should be cut along the grain of the fabric (with a few exceptions). You can tell what the grain by looking closely for the longest line of woven thread. If you sew, you know that you have to buy enough fabric to ensure that all of the pattern pieces are placed following the grain of the fabric before cutting. The extra fabric increases the cost of clothes, but the garment will have a better and more uniform look. If your piece has a pattern to it, a high quality version will have the pattern matched at the seams (think striped pants or a checked jacket).
For stitching, you want to look at flat, even seams. You should not be able to pull apart seams and see through them. Ideally, you're looking for more stitches per inch - tight, neat sewing that will really hold over time and wear. Sometimes, visible hand stitching will give away a very special piece. Look for very straight and even stitching that is neatly finished - whether by machine or hand.
A label will tell you something about the garment through words. But so will the actual material of the label itself. What is the label made of? Are the letters woven all the way through, printed onto a tag or printed right onto the garment (common with t-shirts)? Is it itchy or in an uncomfortable place? It should be made out of a great material, be comfortable to wear and let you in on some key information, namely how it was made and how to care for that item.
For new labels; transparency is the name of the game. Some come with QR codes so you can trace back manufacturing conditions, and information about the company and it's code of conduct. For older labels; the brand, era, and place are going to let you in on the secret. Was it union made? Does it come from a country with great raw materials? What was happening in that country at the time the garment was made? Do they have a strong history of working in that textile or style?
Link to read comprehensive info about vintage labels and how to decode them.
Whether it's a zipper, a button, snap or buckle, this is a great way to indicate quality. Plastic is going to be the cheapest option. Metal can be cheap or expensive, depending on what it's made of - copper, nickel, brass and stainless steel are the best. Does it feel heavy? That's usually a sign of a more expensive addition, especially for jewellery and bags. Is it branded with the name label as the garment or item? That costs more than just buying a generic factory button. How is it attached to the piece? Glue is going to be the cheapest way, and the most likely to fall off. Look for sewn on or studded details that are fastened through the textile, instead of just being placed on the front.
Always check for — and keep — extra buttons, sequins, and other details that come attached to garments. These extras save you time and money if you lose one, and are a sign of quality in their own right (shows thought and care). Think about what you will be able to do to wear it or repair it once some beading or sequins is lost. Those items can be fussy, high-maintenance garments to care for. Don't buy something if you're not willing to put in the time to keep it looking good. When it comes to regular buttons, they are relatively easy and inexpensive to replace - whether because one went missing or because you want to update the look of an item (great for pricey coats and jackets).