Also in some cases (since the new website this year) it offers you seat selection but says it can't guarantee direction of travel. I don't understand how this can work as if you choose a numbered seat, its direction is known in advance, so maybe they reserve the right to change it.
The Man in Seat 61 (
link) has this to say on the subject:
Originally Posted by The Man in Seat 61
Note that the 'choose your exact seat' facility at
www.eurostar.com is 'clever'. If you are travelling alone, it will show all bays of 4 seats around a table (and in 1st class, all bays of 2 seats) as already taken, even if those seats are in fact available. It only shows them as available if you are a group of 2, 3 or 4 people travelling together. If you're travelling alone and want a seat facing another seat across a table (one without a seat back in your face!), you will need to book by phone. If I'm travelling solo I have to book seat 61 by phone rather than online (it's one of two around a table), and I usually do a dummy online booking for 2 people first to prove that the seat is free.
CORRECT WINDOW LOCATIONS: Eurostar revamped their website in 2013, and when you click to choose your exact seat when booking online, the graphic seat numbering plan which appears shows the windows in an incorrect position relative to the seats. The detailed seating plan here is accurate, so if window location is important to you, choose your seat numbers using this accurate plan, then book those seat numbers on the Eurostar website, disregarding the window locations shown on eurostar.com.
... so there is probably more to this than meets the eye.