Thats not true
I picked up an immaculate (I mean immaculate) not a single mark on it, laptop (Dell Latitude 5330 - 12th Gen i5) last month for £254, I even asked him if he could drop his price from £285 to £254.
I paid around £80 less than what other people were selling them for on there for this model (some of the other listings were showing some normal usage marks or minor marks).
The key is to find a good item which has good description, has good pictures, and the seller has sold similar items where people are giving good feedback for those.
Yes you get some odd ball sellers, but i wouldn't say that the site is full of scammers. If you do your checking properly, most of the time it works out.