german trains-online discounts?

There is (or can be) a discount for advance booking, so waiting to buy one at the station is not always a good idea.

This particular journey - pass

DB will sell you only specials Berlin -> Amsterdam or Berlin -> Amsterdam -> Berlin. In this case you have to buy from NS (Dutch Railways).

http://www.nshispeed.nl/

Small problem, the booking form on this page does not work for me. If I use the [book now] buttom on this page it works, but have not found a way yet to change this booking site into English.

Van: Amsterdam Centraal
To: Berlijn Hbf

for a date in May it listed following options
Low-Fixed (Special Hannover/Berlijn) EUR 29,00
Low-Fixed (Discount 50) EUR 50,00
Mid-Flex (Discount 25) EUR 74,00
High-Flex (normal tariff) EUR 102,40

The discounted tickets have to be bought in advance. They are also limited in numbers, thus will sell out at some point of time.
"online discount"
The discounted tickets are also available at the counter (albeit this may add some service fee). But only in advance. Thus as long as you are not already in the Netherlands, online is your only option.

the 29 eur can, starting in AMS, ONLY be sold as return/half, for just a single its 50 eur/minim. And as ever diligent abld tells; can ONLY get those low prices if booked 14 days before travel
and yes, the new NShispeed is VERY much critized in about the whole of Nederland on its very bad faults and booking errors. seems to be the usual: made by people without any train-knwoledge, looks fine, but hardly works. (same in fact can be said for the NS hi-speed, as slow as ever.....
you CAN book via citynightline.com the 29 eur/seats (even longer advacne, but sold out=no more!) but this NIGHT train passes Ber at a very early 4.00 or so (goes on to Praha)
OR try treinreiswinkel.nl, they have the german booking machines.