It sounds to me like they're playing on the relative expense of second hand Apple kit to try and make you think it's a bargain, maybe they paid more than £200 for it and are trying to cut a loss, who knows.
Laptops are harder than desktops in general to sort out second hand because so many of the bits are bespoke to the particular type/model/year, and a lot of what might be easily swappable on a desktop is part of the motherboard on a laptop. (Plus if it's Apple they actively design the things to stop people doing their own maintenance).
Not impossible to get a bargain though, am typing this on a Toshiba NB100 netbook that cost a princely £10 off Facebook as it had no power supply and Windows 7 wouldn't run properly on it (it should have had XP). Add £16 for a 2GB memory upgrade and then a clean install of Linux Mint and it surfs and types fine. It won't do fancy games, HD video or CAD but with 160GB and an SDHC card reader it makes good music/photo store as well. Fires up from sleep in 5 seconds or less and the battery still lasts 3 hours or so.
Just need Linux to sort out Google Drive support though (although Dropbox works fine).