I've probably just been very unlucky, but out of 4 recent Vinted purchases, 3 have had issues.
I bought a top, last day seller was supposed to deliver by I get a message saying they can't find it, must have given it away, sale cancelled.
Bought another top, fair enough response fast on this one, seller had sold elsewhere and forgot to remove from vinted, sale cancelled.
I bought some jeans, seller doesn't post until very last day they're supposed to have sent by. A few days later jeans still haven't arrived, I get a message from seller saying there's been a mix up, sent me the wrong item. Incorrect package finally arrives but I have to return this to get a refund. A week later I get a message from Inpost saying three failed delivery attempts so being sent back to me. Thankfully they must have tried a 4th time as return finally accepted.
All three sellers have 5 stars, because sale cancelled I can't give any feedback. I thought if the seller cancelled a sale it gave them automatic 1 star, but this doesn't appear to have happened in these three cases (I checked).
So now I think you can't trust the seller's feedback as to whether they're actually going to send you what you've bought, only whether successfully delivered items are as described.
At least the 4th item I ordered was great, sat here wearing it now!