I know how to do it m8...thats wasn't the question.
errrrrr....lol thanks that helps...my feeling is that flattening is a quick job but flat and level is alot more time consuming so the cost should be higher.
agree like the weber-set great stuffA decent tiler should be able to sort out walls that are out of plumb himself, everything Chriss has said is correct, myself if a wall needs squaring up and flatenning the safest stuff to use is the adhesive you are going to tile with, i only use cement based addys.
tell him the void behind the tiles is a low emissive air gap and as such is saving him money in heating bills...mate on my road got his bathroom done recently - large tiles. The tiler dabbed adhesive on each corner and sorta levelled em.
Trouble is when there's condensation it brings out the four dabs on each one of his posh tiles. He aint happy..