The simple answer is that it’s the floorlayer’s responsibility to ensure a subfloor is suitable for the product being installed, but it may not be the floorlayer’s responsibility to carry out any remedial work necessary to bring the subfloor up to the right standard. It may be that the work would need to be done by a builder, or a more experienced floorlayer and, if so, the floorlayer should make this clear to the client and ask for the work to be arranged before the installation begins.

In commercial contracts there may be terms and conditions which exclude the floorlayer from this re-sponsibility, but in consumer contracts if flooring is installed on an unsuitable subfloor then the floor-layer almost certainly be liable unless s/he can show that the customer instructed the work to go ahead in full knowledge of the problems and the likely consequences.
Richard Renouf, founder