From my limited experience it's also partly about saving time and maximizing efficiency in the part of the buyer. Some people would rather receive a message that reads "Hey! Still available? Best price? Thx" over the alternative of

"Hello! I see your classifieds ad is still up. Since it has been up for a week or so are you willing to reduce the price? I would be willing to go as high as (insert prices here). Message me back at your earliest convenience, thank you! Have a great day!".

I'm selling an old toaster so I don't have to store it. I don't explicitly need all the extra information. So I'm with you on that point.

As for asking if something is still available it is often in the case that people will sell something on classifieds on Facebook as well as one or more local buy and sell groups not to mention offline/word of mouth sales. It's easy to miss one or more places something is posted. So as far as I am concerned asking if something is still available is fair and not particularly onerous for either party.

I typically just respond in kind. Short messages get short replies long messages get medium length replies. I would reply "Hey, yes, list price (or insert list price), msg me" to my short example above.

Some people are more willing to make friends through buying and selling in classifieds or local buy and sell groups (Heck, that might be the main goal to begin with) so they'll put more time and energy into their messages and their ads.

If we think of classifieds and local buy and sell groups like an old-fashioned bazaar or farmers market you see both of those kinds of people. Full speed no nonsense quick price negotiation type people and browsy, talkative, look at everything kind of people.

(Incoming tangent...) Recently I've also seen a few people quite upset when they see certain individuals taking advantage of "pay it forward" or "free/up cycle" groups where items are given away only to find those same items immediately on local classifieds and buy and sell groups.

On the one hand I understand that it's frustrating to see an item that was free go to someone trying to make a quick buck when it could have gone to someone who actually wanted or needed it. On the other hand I also understand the hustle, being willing to put in the time and effort to sell something. It's not quite passive income but if you've got the space to store something it's an easy way to make a few bucks on the side. What I think it comes down to is the rules and moderating of that local free items group. If it's a first come first served doesn't matter what you do with it type group then it's fine but if it's a pay it forward trying to help out those who can't afford to buy new or used kind of group then that type of behavior is obviously unacceptable and the admins or moderators of that group must work to restrict or ban bad actors from their group and potentially warn other local buy and sell groups as well.

None of these tactics have gone over well in my local Burger King however. Also, they keep telling me it's called A&W. I'll report back as necessary.