I do believe he will not change his mind,can not understand that some people think that ply is just as good as backer board if you get a good deal theres not much in the price I had a good deal once the board was in 8 x4 sheets 12mm thick and the price at that time was £22 a sheet.I remember dan put a comment on my thread before about a tile falling off the wall and killing a kid. Might be worth printing in off and showing the customer and hope they then realise the damage it can cause.