Just remember, never be afraid to ask a seller on ebay for more pics to confirm things, most users if legitimate are more than happy to take some pics to get the chance of more bids on items. and if ever unsure about whether a seller is a legitimate owner, use the old trick of asking them to provide a pic of it next to a common everyday item to give you an idea of the size, you can name the item too.
I usually use something such as a coin or spoon or something like that, obviously would need to be something bigger for comparing to car seats, maybe get them to provide a pic of someone sitting in it or standing next to it and ask for the persons height.
Covers your tracks that you're checking on the legitimacy of an item rather than the size and gives you bit more peace of mind.