Honestly, EBay is what you make of it.
If you want an item that Kato or someone other maker won't run again, that's where you go to find it.
Where else will you find a CR SD45 or similar? Lately I've been looking at orif\ginal runs od SD-40-2's. Why? Because in our heart we'd like Kato to re do them, but we know they are sick of having eastern roads sitting on shelves.
In N Scale things are getting alot more expensive. If I wanted something not made in CR colors, I'd have to buy an undec unit, get it painted, add DCC and couplers...That adds up to a lot of money.
Even as a seller, I have to compete with people I think are idiots who either low ball the price or make it so high, when the buyer looks at you, they wonder what's wrong.
When I started to sell off my HO stuff alot of it just sat there. Luckily E&C Coalporters are a good sell. But the diesels are used but have DCC. Still there are people that only use DC and don't want to get involved in anything DCC.
Over all just use your wits and if you want an item that much, either choose to watch the item and see how it goes or move on. If you go to your usual source for supplies and it's sold out already, then EBay will help. Lord knows, in N Scale buy it quick if not have it reserved or it's good bye Charlie.