How can this advert be legal in any way?
That particular one isn't....
CAA Guidance is: "but it should be made clear that it is a cost sharing flight, and not commercial air transport under an Air Operator’s Certificate (AOC)"
This person states that they are offering an Air Taxi service (implied AOC), without a valid CPL and without an AOC, therefore technically liable for prosecution under current laws.
CAA Guidance on Cost Sharing
This is the official guidelines. No 20 pages to flick through, no messy, lawyer talk, just plain English. Something tells me the NZ CAA has been over and taught the UK CAA to be more accessible to people...
The questions are: Would you let a complete stranger, non-pilot, sit right next to you with a complete set of controls? (Do you know their mental state? Could they ruin the fun for everyone? etc...) Would you cope with the pressure of having someone used to flying from A to B with Easyjet, pushing to go in marginal (or worse!) weather? Would you cope with them feeling unwell during the flight? (some of my friends haven't felt all that well in a light aircraft going through light turbulence - it seems surprisingly common...) Is it worth the risk?
For some people it might well be, for others it is quite scary. I am not sure I would want to offer my flights to complete strangers, without at least a faint knowledge of who they are!