I've bought almost 20 pairs off StockX within the last year with only a few issues like a damaged box or a lace having a smudge on it (both of which they refunded me partially for)
That being said, if you are super picky, you may not be satisfied.
You obviously can't see the photos of the pair you are getting through StockX.
So if a toebox isn't perfect or you end up with swooshes/toeboxes that aren't matching tumbled or smooth leather, you'll be stuck keeping it.
On the other hand, they guarantee authenticity.
Whereas with eBay/social media, you can see detailed photos and talk with the seller, but you'll have to do your own legit checking.
If you can get a pair on eBay for cheaper or same price as StockX (and feel comfortable doing so) that is the route I would choose first personally.