I feel the clothes and the seams. After a while you get a feel for premium materials and construction. I also look for known brands that make BIFL quality gear, but seriously the picking not up and feeling it test works great, if it’s an older garment and it is undamaged and feels sturdy, it probably is. Also check all the sweaters for anything 100% merino wool or cashmere, I have some pretty “nice” fancy sweaters I use as warming layers under my outdoor gear. $2 for someone grandpas cashmere sweater or $120 for a comparable smart wool.

If it has zippers check what kind they are and the brand of them, for mass produced stuff ykk makes the best zippers, there are a couple of zipper brands out there for high end and premium labels that are as good or better, but I’m not sure of all their names, but in general a ykk is a good sign.

For “waterproof” or outdoor gear, look to see if it is “seam-taped” by looking at the seams on the inside and checking if they have been sealed.

What kind of garment or gear are you looking for specifically, I might be able to give more specific suggestions.

Some of my best clothes were thrifted. I shop a lot of places, but the highest quality clothing I've thrifted mostly came from private church thrifts or Junior League thrifts. Don't overlook consignment second hand type shops if you are shopping specifically for a professional wardrobe.

Learning about fabric is a biggie, and I have no shortcuts to offer, all require time & touching the good stuff. I've sewn since I was a kid, so spending time with fabric is something I grew up doing.

You can go to a high end department store & look through the clothes, particularly the business wear. Feel the jackets, pants & skirts. Good suits for both men & women have a minimal amount of manmade fiber. Touching a pair of jackets where one is 100% wool and the other 60%/40% will give you a good lesson that no internet or book description can match. Nice infographic with lots of names you might see on labels: https://sewguide.com/textile-fibers/

Know which brands actually last vs. are trendy and popular. How does this shirt you know was popular two years ago look in the thrift store? that low end fast fashion stuff will teach you just as much because you can see what to avoid. Find two similar items & compare them. Look at the seams, look at fiber content, look at what wore out/ tore/ stretched badly.

Personally I look for Ralph Lauren for both me & my husband, Geoffrey Beene for him, Talbots for me. There are other good brands, but these fall into our specific 'will always fit' (hubs is a XXLT) or 'will always suit my style & work dress needs'.

I wish you luck!

You need to find brands you know are good for you then thrift them. I prefer LLBean dress shirts. I always look for my size, and even go to EBay. $20-$25 for a gently used shirt is better than $60 new

It's mainly getting a feel for the fabric. Does it feel thick and durable, or thin, stretchy and brittle? Are the seams sewn straight and evenly? Hold them up to the light and see if the light shines through the fabric evenly, or if there are thin patches, this is likely where the item will tear. Like I want t-shirts that wash well and wear out evenly, so they get that super soft feeling as they get older. Has the fabric aged nicely, or is there a lot of fuzzballs and pilling, especially on synthetics, which might also suggest the previous owner didn't care for it properly (like washed and dried it at too high of a temperature). If it's something that is supposed to have some stretch like athletic wear, you can sometimes see that the threads of the stretch material have snapped like little broken rubber bands, the fabric should look uniform and smooth. Check how it's supposed to be cared for, personally, I am against dry cleaning from the environmental impact, but it's important to look at how it's cared for. Older clothing often required ironing, starching, and pressing, but there was also permanent press which usually didn't wrinkle as easily and had pre-set seams. Now clothes are more wash and wear friendly. Will the garment care require more time than you are willing to commit to it?

I will lay clothes out, fold them multiple ways, see if the garment is symmetrical and the seams line up. Lower quality clothing from overseas, it amazes me how uneven they are, no offense to the people who made them. Older clothing may have a union label or logo on the tags. There might also be quality control or inspector numbers on the tag, which means someone actually hand inspected the garment for quality. Prior to about the 1980's, a lot of clothing was handmade, and I've found those clothes to be superior quality, since hours of work was usually put into making a single garment. So they'll feel very well made but not have any identifying tags.

Also with thrifting and BIFL on a budget; I learned how to hand sew and am trying to learn how to use my sewing machine so I can tailor and alter my clothing. Nothing makes a garment look more flattering than tailoring it to you, especially dressier or business attire and jeans. It's also helpful to repair things like buttons, zippers, and patch items. Upscale department stores used to have an in-store tailoring service. You would buy a garment, know your measurements, and the tailor would personalize it to you. Now, you can learn to do it yourself and give your clothes a very customized fit. It's good if you find an item slightly too large, you can take in the seams a bit, or add darts, for example.

You also want to look up tricks to identifying and removing different stains. Most food stains can be removed, but I'd avoid anything that looks like mold or a possible bodily fluid. Yellowing of white fabric is also often permanent, but there is a product called bluing that will tint whites slightly bluish to make them look a brighter white if the yellowing/dingy color is only slight. Sometimes hanging them outside on a sunny day also brightens fabric, and remove some odors that washing didn't get out. Maybe it has been in a dark closet for too long and picked up a musty odor, but airing it outside can help. Heat from the dryer will often set in stains and odors, so if one wash didn't get it out, try washing it again before drying it.

It's helpful to go to the thrift store often, know when they put out new items, sometimes expect you'll go home empty handed. It seems like thrifting gets almost competitive during economic recessions.

My advice is to look your buys over GOOD. I sometimes miss things like stains or torn seams.

For denim specifically, I look for 95% cotton or above (this info should be on the tag). Less spandex means it won’t stretch as much, and will last me longer.

Dumb advice, but it's served me well when I've been thrifting. Just because something is a good deal, doesn't make it a good deal for you.

I've weirdly been more dissatisfied with clothes I've bought that were either on sale or thrifted where I've said "I'm not crazy about the look/feel/fit, but I can't pass this up." than I have been with some more expensive clothes that I really took my time/save up for. And I have some really good thrift/consignment buys. Not knocking that at all, just saying that you can pre-Kondo things sometimes.

Having said that, I try to find a 3 way or 4 way seam, and pull gently on the different pieces of fabric that lead into the seam. If you have a sense that the stitching is going to pull loose, put it back. Read the laundering directions and make sure that the thing isn't dry clean only when you didn't expect it to be.

I'd avoid thrift rain gear - even the good stuff has coatings that wear off and it's very difficult to tell.

You are asking too broad a question. Men, women or children? Multiply by casual, play, dress, skirt, suits, pants and 300 other types of clothing. I get your question. I do. But there is no answer as the math is too high.

If you have any hope of finding great items at thrift stores you only hope is a smart phone while shopping and even then its a mixed bag as you can find a titanic quality Brioni suit that sold for $10,000 new, but it was sold new in 1984 with collars wider than the tires on your car. Quality does not mean you can actually wear it as fashion plays a role. The stories you read on the internet about people finding $10 Alden shell cordovan boots and $15 Jean Paul Gautier sweaters are by those who are hyper focused/smart in one clothing type and are in an area with fantastic thrift stores.

It’s kind of a learn-as-you-go adventure. All these advises are great. Enjoy the journey! 👕👜🥾🧥