I just want to share an experience which almost ruined our trip to Agra recently.
We had booked etickets well in advance for the Shatabdi Express train which leaves Delhi for Agra at 6.15 am returning late evening. We brought copies of the etickets with us as well as our passports.
Arriving at the station we were asked by someone to show him our eticket before we got to the platform - he told us that we needed a boarding pass to be allowed to board the train, and we would need to go to Connaught Square to get one as the office in the station was shut at the time.
I was absolutely insistent that we would get on the train, so we did - and fortunately all was well. We later found out this is a common scam; the person tries to make you miss the train you are booked on then arranges to drive you there at great expense.
There are warnings about not handing your ticket to anyone once you get on the train, but these are a bit late to be of any use.
So, just be aware - a tourist at Delhi train station early in the morning is an easy target. We were travelling with children so probably even more of a target.