The advance tickets all come from the same pool all the same price when bought online or at the station
Er..... no. Some
TOCs▸ offer a discount on their own Advance Purchase fares if you buy them from their website.
East Midlands Trains - ^1 off.
East Coast - 9% discount.
First TransPennine Express - 16-25 Railcard holders get 50% off, instead of the usual 34%.