I was offered a 168.027 locally in really nice condition, brick bracelet and all, for 700 euros ($800). Since I'm looking to resell and make a little profit, I had to turn it down. Realistically, as mentioned above, these should go for $1-1.2k when in good condition.
The thing with eBay and C24 is that there's fees which you'll eventually end up paying. A lot of sellers sell on both and keep the prices pretty much aligned, maybe minus the fee difference. So you're not going to get great deals if you don't follow auctions for weeks or months and when you end up winning one, hope it's better than the shitty photos and a paragraph of AI generated description.
Your best bet, I think, is this forum. If it's not a watch you need tomorrow, you can be patient and check the sale listings frequently. Maybe set a saved search on eBay too for auctions only and get notified when something comes up.