I do vintage and look at yard sales, consignment shops, thrift stores, online places etc. I see a lot of vintage modern stuff and there are a few things to consider to figure out if they are worth anything.
Condition. Modern clothes need to be in good to very good condition. like new is ideal.
Fashion. Are they in style now, or at least still worn by people even if they aren't shown in magazines and on current tv shows. Could it be in style with a few modifications. simple ones. Classic pieces are obviously always in style and this doesn't apply to them.
Original price or designer. If it was expensive to begin with or a designer item, then you can probably still get decent money for it regardless of whether it is still in fashion. As long as it's not considered tacky or out of style, then you can sell it.
Vintage items are different, as are vintage reproduction and vintage inspired. Also, niche market styles as well. you need to look to specialty places for them. For actual vintage items, talk to someone who knows what it will go for.
If you want to sell regular clothes that weren't expensive then you should try looking on Facebook for a yard sale page in your area. You can post a photo of the items on there and your price underneath it. Look at the other items for sale and price yours similarly to similar items. You'll get more there than you will having a yard sale, believe me. I'm one of those yard sale people and I will walk away if it's clothing more than a dollar. unless it's vintage and ill pay a little more but not too much more, and like a lot of yard sale people I'm great at explaining to the seller why it's not worth the asking price. Folks go to sales for bargains and the people who look at a fb page will pay more.
I'd only do test or eBay if it's expensive or vintage etc. I'd do that before I do a consignment shop. If you don't know what to ask for it, take it to a consignment shop, tell them you're selling it online and ask what to price it. Actually price it a bit lower because they may tell you a too high price so you'll bring it there when it doesn't sell, and they can make the profit.
I just give my old stuff away. I've also heard of clothing swap places online and you can swap things. You might could swap several old outfits for one newer or nicer one, etc. Never been to one but if you can find them PM me and tell me about them please. I sometimes only check pm here.
If I can help you out at all, pm me. If you want me to look at some photos and give you an idea, pm me and ill give you my fb info.
But check out local fb pages for used stuff too, to get an idea of what sells.
Good luck! Let me know if I can help. Just because we disagree about some things doesn't mean we can't get along about others. I don't buy anything new if I can help it, so this is my thing.
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I'm giving it another shot. We will see.
My forum is still there and everyone is welcome to come join as well. There is a private women only subforum there if anyone is interested. Also, there is no CAPTCHA.

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http://www.rightplanet.proboards.com