I've bought and sold on Vinted. You have to look at the reviews and be quick if you want something. I lost out on 2 decent things last week for procrastinating. I picked up a lovely black jumpsuit for work from Whistles for £15, was originally £150.
I've sold a lot of things on there. I am one of these people who buying nice things from decent shops, with nothing to go with it, inappropriate for my lifestyle, and it hangs there for 2 years. I'm working on this! One woman messaged me in a bit of a grump saying my things were too cheap! I was a bit embarrassed.
Some people do have a bit of a nerve though. There are some cashmere jumpers on there that come from companies that sell them for £250 and people are selling them with holes in for about £50.
I usually just look for things for work on there as I don't want to spend lots on clothes for my job. Also, I look for nice to haves such as Sweaty Betty after workout tops.
I sold a designer item of jewellery once and the person who bought it wrote that it was a fake on reviews, but didn't ask me for a refund, or challenge me on it. I got very upset about that, and went to great lengths to get proof that it was, and then responded to her under her review. It made her look petty.
You have to cut the wheat from the chaff and be very specific about what you are looking for.