Moved to Forum Feedback. Fits better there. I'm assuming this is about the classifieds on AF-UK. If you're talking about how you tell whether a gun is second hand vs. new, then let me know and I'll move this again.
It will say 'sold' if a seller has marked it as such, but 'uncompleted' simply means they haven't 'bumped' the post in a week. It might be available, they might not be interested in selling it or they might have forgotten to mark it as 'sold'. 'Uncompleted' basically just means the seller hasn't interacted with the advert at all in the last 7 days so we have no idea which of these conditions it is.
Have put a lot of thought into how to make this less misleading, but all the other options seem to make it even more ambiguous.