But the total to-pay amount appears before you click book, so if you don't like it you can choose not to purchase the flight(s).
I'm looking forward to my GLO-JER flight next Friday. Hopefully it'll be on the D28. I've got two more in Sept: BHD-IOM (£15 including taxes) and IOM-LBA. I'm hoping to get on both the L4T and the SWM.