I am still wondering how to modify threads/posts in the marketplace section. Or do you have to close them and start a new one? How does this work? (even closing, you have to ask it, or how can it be done?)
Closing of your own marketplace threads is addressed in the new update rolling out, hopefully, by the end of this month.
As far as editing goes, there are time limits on this.
You are more than welcome to always report a thread of your own and ask for it to be deleted or edited for privacy. Most of the time, we'll happily comply with this request. You reporting your own posts does not have any negative impact on your account.
I think all sales threads, both original thread and all replies should be open to edits.
On other sales message board websites the common protocol is to list a domain for sale and once sold to manually edit out the domain details and price.
Personally I don't feel comfortable buying or selling a domain that has an archived thread
Archived threads have very little, however, to do with the real value of a domain name. The age of a name often times also does not have much to do with its value. A premium domain name is premium. Most of course are junk.