In 2015 I started selling export surplus clothes (these are clothes of famous brands that have some minor manufacturing defect in them so we get them from the factory for very cheap). I used Facebook groups a lot. What I can suggest from my experience is that if your photography is high quality, you will get more people interested in buying from you.
You don't need a high end professional camera for this. You can use your phone camera with a little bit of editing on Snapseed before posting them.
I used to post pictures on the group from Thursday to Sunday. And I never mentioned prices. I would write "for prices and pickup location please WhatsApp: xxxxxxxxxxx) So when someone messaged me, I would save their number and add them to a WhatsApp broadcast list. Even if they didn't buy immediately because of the weekly new arrival update messages on Whatsapp sooner or later these people converted to customers (it's like retargeting ads).
Since these are used clothes you'd be selling, you can brand and market your business from an eco-friendly, sustainable fashion, upcycled etc angle.
One thing I would suggest is, get your stock of used clothes laundered, ironed and packed like a brand new apparel. Also put your own branded hangtags and price tags to them. Don't wait for "first let me sell this and make 500 dollars, then buy more and make 1000 dollars". Go all in. Invest a little bit of money into branding it right and if possible do pop up shops / stalls in any fair or event you can find locally. Also offer delivery service.
Don't let anyone convince you that this business cannot become big. I pretty much started the same way (except that mine was unused clothes with defects cuz in my country people are not open to th idea of wearing used clothes). Now my business has grown into a brand with decent sales online and I also have two offline shops.
Check "Uptown Cheapskate" on Google. It's a big business in USA that sells used high end branded clothes.
All the best brother
