I'm not sure you can remove them..I think you just have to update them..i.e. sold, still avail etc. I think you only have 1/2 hour after posting to either delete or edit your post
image at the bottom lefthand corner of the post you think requires reviewing by the staff. In the process of reporting a post, you will be provided with a place to enter a question or comment to go along with your report, this will only be visible to BRS staff.
The above two posts are also correct in pointing out that BRS policy is not to edit or remove much of anything once it has been posted unless it is found to be in violation of BRS rules and/or policies, or, as sometimes happens, someone posts private information like their telephone number or address on the open forum (never a good idea on any publicly viewed open forum) and thinks better of it.
There are exceptions, they are not common, but no harm can come from asking, so don't be shy of asking about it either.