I am a lover of Birkenstocks and have been wearing them for most of my life.  I have metatarsal arch problems, and the shaped soles support my feet wonderfully.  I bought the last paisabout 5 years ago, and this year I decided to buy a new pair.  I bought the same European size (45 M) and it seems as if the new pair are too big for my feet.  The quality is the same, but there seems to be an extra 1/2--3/4" in length.
It is possible that the sandals will change size as I "settle" into them, but for now, they are strangely large.
Everything else is as expected, and the seller wasa right on the ball--excellent seller.