(Topic credit: +Andria Perry in the discussion of https://blogjob.com/groceryshoppingwithcoupons/2016/02/28/save-more-money-2-clothing-and-more/ . Image credit: a charity known for organizing excellent stores, and other good works.)
"S/He buys all her/his clothes at secondhand stores" may suggest (to older people) someone who is very badly dressed. If you don't have a lot of time and money, it may seem that that's the effect you'll get by thriftshopping for clothes, because the selection is usually limited. Over time, however, it's possible to build a wardrobe of upscale classic clothes entirely by shopping at the resale stores that support charitable causes.
There was a time when a "fashion blog" featuring pictures of what was in my closet would have been quite the hot ticket. As a Bright Young Thing I was considered well dressed--and I always shopped for causes. That time is over. I'm no longer twenty-five years old, and the look that works for me is no longer the height of fashion. I can explain what worked for me, but finding ways to make it work for you will still be up to you.
First, it helped that I'd absorbed a certain level of "fashion/beauty consciousness" as a child. Apart from what the Madison Avenue Misogynists are trying to palm off on women in a particular season, style rules differ because most people can achieve more than one look that they may like. As a top-heavy young woman in Washington, D.C., I considered the fashion looks that worked for Barbara Bush, Dolly Parton, Marla Maples, Rekha, and Meredith Baxter-Birney. Then, being in Washington, I generally bought the sort of styles that worked for Mrs. Bush. Even if you are a top-heavy young woman, that might not be the look you want. The point is to have an idea of what you do want.
The next step is to find it in secondhand stores. If you're committed to buying everything you wear in aid of a good cause, you may have to wear compromises for a year or two even in a city, but you will eventually get the wardrobe you want. I'm not talking about "the 'exclusive' style that only Mary and Jane are wearing this year, and the store has only two left, one in each color, and this color is mine and I want it." (That may or may not ever turn up in good condition in a charity store.) I'm talking about a reasonable number of shirts, jackets, skirts, trousers, sweaters, dresses, overcoats, etc., that work for you and won't scream "this year" when worn again next year, or next decade.
Look for quality and condition. When a dress shirt costs only $2, you might not mind that threads are already starting to break and pull out on the inside, especially if you're going to wear it under a jacket anyway, but over time you will notice that the $3 shirt whose seams were solid has lasted longer and given more satisfaction. As a general rule, anything made from rayon or polyester is worth buying, even on a dollar-a-bag clearance sale, only if you're planning to use it in some sort of craft project rather than actually wear it. Natural materials are almost always best. Pretentious neighborhoods (Chevy Chase, Maryland, comes to mind) may frown on charity stores; nice neighborhoods (Bethesda, Maryland, comes to mind) tend to have great charity stores, where rich people share and circulate treasures collected around the world.
Over time, you may notice that certain labels tend to recur in your favorite bargain clothes. They will probably be upscale labels, no matter how casual your style is.
When you have a choice between something that's fashionable right now and something that's less fashionable but that suits you, as a general rule the item that suits you is the one that will give more satisfaction. Even if you hang out with people who take fashion seriously, and they tell you you look like a ghost from the past, at least you'll be a happy ghost. However, all rules have their exceptions. If you're going to spend time with someone who feels less confident about his or her self-image than you do, thriftshopping gives you the option of varying your look to include something that suggests that you're trying to look like, rather than upstage, this client or friend.
How do you get the time for all this thriftshopping? It helps to start early--as a student, if possible. I did odd jobs that often gave me a half-hour or an hour to kill in neighborhoods that have good charity stores. Which neighborhoods those are will depend on your city and your preferred charities. If you can get a part-time or occasional job providing day care for a child or patient who enjoys thriftshopping too, you're really in clover.
After finding good stores, the third step is knowing when to stop. Charity stores sell a little bit of everything. Young "nest builders" need a little bit of everything to replace the hand-me-downs, borrowing, or lack of things they want. Because buying things from a good charity store is a way of supporting a good cause, it can be addictive. I'm generally in favor of a reasonable level of hoarding, but if you have more than 100 complete outfits for each season, have so many "decor" items that you're starting to stack ceramic pieces in layers on the floor, or have the supplies needed for more craft projects than you could reasonably plan to finish if you worked on them daily until your hundredth birthday, it's probably time to donate some merchandise to your favorite charity store and just send them money instead of shopping...or else open a charity store of your own.