Since latest WOTLK update there is a good 6-10sec delay when I sell. Post button will grey out for a time. Just started. Reinstalled the addon and deleted settings.

Auctionator for Wrath Classic greys out the post button while waiting for when it is sure a post will succeed and then the post button will ungrey. Normally this would be an insignificant amount of time, but with the pre-patch and increased load on the servers the delay has become very noticeable. There isn't a good solution.

I wonder why that is, the default blizzard sell works instantly every time

Wrath
Indeed, Blizzard's sell interface can be published directly
Publishing on Chinese servers now requires a 30-second wait

Got a solution, don't grey out the post button and let the user quickly retry if the post fails. Available in the latest alpha
Auctionator-9.2.36-1-g1a13343-wrath.zip