List used items for sale with just 3 clicks and no thinking about the details. Make it maximally easy to get rid of stuff you don't need but can't bother taking the time to sell.
Current options require filling out forms and describing each item you are selling. In contrast, this solution makes it as easy as sharing a photo on Instagram. 3 clicks and done.
Provide additional information about an item only after you already have a prospective buyer. This increases the motivation and makes the additional work seem easier. The buyer might not need any additional info other than the price and where to pick it up.
This would make sense as a good feature to add to any existing classified ads / 2nd hand marketplace. After having created an account with the classifieds marketplace that offers this feature, you would install the feature's shortcut on your phone's home screen.
A 3-click feature (not counting the phone unlock):
click on the feature shortcut
click to take a photo (or a video walk-around)
click to post it
People looking at the ads would see that the item was posted using the 3-click feature so they won't expect to see all the details right way. They wouldn't consider it shady that more details aren't available. They know how it works and will subsequently request whatever info they need to know.
An AI attempts to identify the item and sets it's title, category, brand & model, etc, with as much details as it feels confident. Upon posting the item, you get to select (if you want) any of the AI's suggestion that best match the item. You don't have to bother though. The AI will just use whatever turns out to be the most likely match.
If a buyer wants more info about an item fast, they can request it by selecting one or more of the pre-defined requests, such as: price, year of make, brand and model, where & when can I pick it up, etc.
In the event they need any additional information that doesn't fall into pre-defined requests, they know that they may have to wait longer for a reply because the seller might be busy.
All the info that is eventually provided by the seller, gets included in the item's description so that subsequent people who might be interested see the info without needing to request it.
The sellers don't have to bother figuring out an appropriate price for the item being offered for sale. They can configure their settings to something like:
price matching similar items being sold
10% below the average of other similar items being sold
50% below the average price of new similar items
The buyer does price research and sends an offer with reference links.
Reducing the number of steps
If you sell used stuff for a living and do this frequently enough it would make sense to reduce the steps even further. You could port the app's feature to your volume-up/down button. Upon holding it, the app would launch in ready-to-take-a-photo mode. You take the photo, and confirm to post it.