Any chance this constellation is legit?

Did you notice that the pictures are of two different watches? Look at the crown in the movement photo then in the other photos. Not to mention that hexagonal crown is hideous and not original. The dial looks like someone tried to clean it, look at the scratches between the markers. There's a lot a I don't like about this watch, and the seller comes across as dishonest. I'd avoid it like the plauge.

The movement picture is of a 14393, I'd guess, with a cal 561 date movement.

Now, to the watch: Dial isn't in a particularly nice state, but I guess that's yours to decide. The bracelet doesn't belong on the watch and is from a much later period. 400$? More like 100$, I'd guess. The crown is funny, actually, looks like it's from a Seamaster XVI Olympics, the special edition made for the games in Melbourne in 1956. That'd also explain why it's rose gold, not yellow gold, and thus doesnt match the watch. Case is polished, but we've certainly seen worse. Oh, and the "box" is merely a regular Omega service pouch, used until quite recently, which doesn't really carry any value.

I’m also slightly concerned about him stating it’s a cal 501. While COSC-501s can be correct for 2852s, I believe pie pan dials in them always came with 505s. Not a 100% sure on that issue though.

Judging from all the fluff in the seller's description, I'd guess this isn't exactly a bargain, but do you want to let us know how much he's asking?

Yeah, no.