Your part right, every boat having a measurement cert won't stop cheaters. However it plays a major role in catching them out. Non conformance to measurement certificate is the way that a boat would be protested to be able to dish out penalties for cheating.

Having the manfacturers supply the cert is the simplest way to supply certificates. Any part eg. Sails and mast could be approached the same way and just added to the cert. At the moment I have been writing the measurements of the sails I build in the tack. Makes it easy for the measurer to check the figures that way. Most sails come from the builders as well so it's easy for them to do.

The role of the class measurers would then be to measure a boat if a protest occurs.