GOAT, I like it... it gives pics, and you can try to negotiate price or buy used.
StockX seems legit. l bought a couple pairs from them, but their business practices are shady AF IMO. I would buy from them again however, they wouldn't be my first choice. Here's a link
https://niketalk.com/threads/has-anyone-else-been-using-stockx.644042/ decide for yourself, the back half of the thread is where the shenanigans start.
Stadium Goods ( just bought 2 pairs from them and they look good) the first time I ordered the 11 i.e cobalt, and they sent me red 2 retro lows, they quickly fixed it no hassle at all.
And of course Flight Club.l but prices are
I've bought from all places, and been satisfied with merchandise legit wise. GOAT and StockX have the cheapest prices though.
Edit: Sneaker Summit
https://sneakersummit.com/shop/ has a huge in store selection, they're based in Houston (I've been in store) that all look legit. I've just never bought from them.
Never dealt with Kixify maybe someone else here could help on that one.