do sellers overstate the condition of goods?

Yes, yes they do! I always try to keep in mind my own experiences buying on eBay when I look at my buyers "feedback left for others". Sometimes it's the buyers are unreasonable, but often it's just that they're unlucky. You see it most with people who regularly buy cheap stuff, there's a few private sellers who have the attitude that if something is cheap it doesn't matter how they describe it.
I buy quite a lot of clothing on eBay and I've run into quite a few "was described as new but isn't" situations myself. Sometimes the cheapest isn't always the best! After a while you learn to steer clear of anything with a description like "still lots of wear left" for example.

I think sellers, especially private sellers or business sellers pretending to be private sellers are the worst culprits for this.
Its happened to quite a few times over the years, have had 3 items already this year alone from 2 sellers.
bought 2 items of clothing from a pretend private seller item specifics were brand new ,as i was using the app i didnt read all the description, my fault i know but when they arrived they looked washed so looked at listing again on my computer and it turned out items had been worn once. Now i was happy overall tbh but cant understand the mentality of someone who cant see the difference between used and new and unused.
The other sale a used item of clothing in good condition. Arrived and there were substantial rips in two places, but again a private seller buying to resell who hadnt really bothered to check the item over at all before listing.

my biggest problem i guess is those who list as new when its been used/worn ect , i mean its not rocket science to be able to know if something has been used or not.

I have recently been having a clearout and been selling stuff on, a few items were new with tags but because they had been sat in my wardrobe for a few years i sold as used.

The amount of times I have been browsing with a view to buying and the item is stated as new and then the item description states "Worn once, immaculate"...so that wouldn't be NEW in my opinion.
One person is selling used makeup....granted, you cannot list it as used, but that's revolting.

As a seller, I literally examine every stitch, photograph ANY and ALL possible faults if there are any and highlight this and tell the buyer to look at photos x and y to be sure they want to bid. I take photos of the size and brand label and the care instructions/composition of material too.