Improve messaging to sellers about how Unavailable works, or unblock Custom Offers the Seller sends

[moikchap]

It's happened a couple times now that a seller will send me a custom offer, and then probably because that work would put them at their limit, they immediately turn on Unavailable.

While in Unavailable, I can't accept the offer, and I can't tell them that I can't accept the offer. The sellers probably think they're just blocking future orders, and not the one they just sent. So now the order has to wait out the status, and they're probably sitting there wondering what the problem is, and I can't tell them. I'd have to go digging for the prior incident to see what the message was when the offer was sent, but this time the seller said "Feel free to accept the offer whenever you are available." which pretty clearly indicates to me that they aren't expecting to be blocking the offer they just sent. My gut says there was a similar message last time from the seller last time this happened.