Although drifting off topic, the Severn Beach line is not a "buy on board" line, hasn't been since January 2023, though as you say, Severn Beach it self has no facilities. Other stations on the line do have have facilities and are PF stations.
Guards will sell tickets on board this branch as will roving Ticket Examiners.
Tickets will be sold first for those travelling between Temple Meads and stations inbetween to Clifton Down and then a second sweep will take place selling tickets for those travelling to Stations between Clifton Down / Avonmouth & Severn Beach.
Clifton Down being the fare change point from £1.60 and fares beyond £2.00
This is done to avoid wasting time changing the destination for each ticket sale, the downside to this is that Clifton Down and Severn Beach will have an incorrect and high amount of journeys recorded as ending there when in fact they haven’t so Annual
station usage figures published by ORR will be skewed!!!!
This branch is subsidised by the local authority hence the cheap fares that even some are reluctant to pay!!!!