Wrong. They should design for 230V +/- 10%. You DO NOT design for 240V. You design for 207V to 253V (minimum range) and you call it 230V.
Then you'd get the sack. You would need to design it for 230V +/- 10%. It must work and be safe at 207V to 253V. It must work in all European countries and it must work for the full range of possible voltages within those countries. Protective devices and ratings should be OK at the nominal
230V. Their ratings already incorporate the fudge factors to be safe as a resitive load at 253V. i.e. a 13A @ 230V resistive appliance is OK on a 13A plug, because the fuse, socket and plug are rated to provide protection at 14.3A @ 253V.
It WAS commonplace. It is now not permitted to design such appliances, except for incandescent lightbulbs. You would not get a CE mark. You would not be able to sell the product to a consumer within the EU.
Christian.