GWR auto-trains introduced wayside "Halts" in the 1920s-30s, the difference to a station being they had no staff, and the guard sold tickets (generally described as "like bus tickets")directly to passengers from these. When there was more than one coach the guard hopped out at the station and directed any waiting passengers into his own coach.
There were also oddball arrangements at these Halts for the guard of the last train before sunset to turn the lights on, and the last train of the day to turn them off (sometimes delegated to an alighting regular and reliable passenger).
It seemed to me to be in the 1970s that TTIs as a separate position on main line services were merged with guards to create conductor-guards. Until then guards were meant to keep a lookout for signals through their periscope and guard the mails and parcels, not being involved with tickets. TTIs seemed to work to a regular pattern rather than "snap" inspections on main line trains; on cross country services with multiple stops they always seemed to appear at the same place. They used to resolve all sorts of issues for passengers, who never really saw the guard, even to the extent of throwing notes out when passing signalboxes, to be telephoned forward. I never saw this last activity myself but have read it described many times.
