Questions about Watchbox

[Mr Supernatural]

Hey all, first time member and first time Rolex buyer here.
I recently engaged Hans Singer at Watchbox for a trade. I sent him pictures of a Omega Seamaster and got a commitment for $1200. The watch I was trading for was a 2020 Datejust 41. The Datejust was priced at $6800 plus tax plus and my watch. I sent the watch in and Hans got back with me after the inspection and said he could only give me $500 for my watch.
He offered me the Datejust for $8060 plus my watch.
Questions I have are is this a good deal and is Watchbox reputable?

Hans also said that he did not receive the warranty card with the box from my Seamaster. This is very disturbing because I know that I sent the warranty card at FedEx. I took a picture of it before I gave it to FedEx. Which makes me think that Watchbox is not reputable.