I completely don't support The Trainline. Absolutely no need to pay a booking fee if you book through the operator directly, plus you're sometimes eligible for discounts (ie what used to be EC 10% web fare discount), also with booking through VTEC you get your WiFi code in Standard, plus Nectar points etc etc. That and the previously mentioned ability to change your reserved seats/coaches.
With regards to forward/backwards facing seats, it depends on the circumstances but they can almost never be guaranteed - with the likes of TPE 185s going on various routes across the north, it's easy for sets to get turned around during normal working.
Longer distance operators such as VTEC and VTWC *usually* have First at the London end with Standard at the Country end of the train - however again this can change at short notice. Newcastle around the bridges is something that does occasionally happen if there's something affecting the train from the DVT end.
In terms of your complaint, you'll only really be able to complain about the double-booking.
RE: What's annoying you today? V4