Just gotta say I'm thankful for this thread, it's helping me learn how to write better eBay item descriptions and include better photos!
Just remain factual, concise and avoid trying to "tart up" the item you're selling. By all means describe the condition if it's not already clear from the photos but avoid using terms like "mint condition" because it's all relative. What might be "mint" to some people is far from the dictionary definition, especially if you're talking about a used item.
If there are faults or flaws with the item, even if it's just a scratch or there are some marks due to regular use, then say so. It's not just about what you say, but also what you
don't say. If I see a listing with barely a sentence, I usually skip it because to me, the seller is being dishonest or deliberately trying to hide something.
That being said, don't go over-board, having sold thousands of items over the years, there is one thing I've noticed and that is people are stupid and don't read what they are actually bidding on. For example: Shipping -- If it's a large or bulky item that is impractical to ship, I will clearly specify in coloured, bold, underlined text that the item is for "pick up only from
x location on certain days, between certain hours" but I can guarantee I'll get some muppet who will ask for a shipping estimate or they'll bid on it (and sometimes win the auction) with no intention of picking it up.
Also, don't use ebay wanker buzzwords like some of the ones mentioned in this thread. It's not only cringe-worthy but it makes you look like some kind of shonky used-car salesman. If I see a listing full of crap like that and trying to make something appear "rare" and "unique", I won't bid on it.
Final tip, take your own photos, don't just copy stock product photos from Google image search. People want to see the actual item they are bidding on, not a photoshopped marketing image. Again, it comes down to your reputation, if you're copying someone else's photos, I'll be thinking you are trying to hide something.