When you edit the first post, you can either highlight a line or lines and use CTRL+S on the keyboard and it will add a strikethrough that line OR find it in the toolbar on a mobile (first set of three dots I think, it an S with a line through it.)
I mention it, as some do that to sold items to make it a bit easier to see what's for sale still.
others use a pale grey, or make it small text etc..