One thing the promoter can guarantee is that somebody won't like the way the gig is organised.

I have never been involved in an Unthanks gig so don't know how their tour was organised but a typical tour is set up between the agent and a number of promoters who either own or hire the venues. The choice between flat floor and concert seating would be down to the promoter who is paying both the band and the venue. Its only the band's call if they are paying for the venues themselves.