Whilst I agree completely that any responsible owner should check that their vehicle is within their specified payload I can't vouch for others, some who I know admit to 'probably' being overweight to some who know for a fact they have virtually no payload. Overweight Motorhomes – How To Avoid This Too Common Problem – MotorhomePlanet.co.uk .
When I was getting my front axle uprated, this was paid for by the dealer after Rapido's answer was the vehicle was within the spec. quoting things such as the factory 3.0 litre engine was an extra 50 kgs. The front axle weight limit was 1850 kgs. it weighed very close with a full tank & 2 people in the front (we are normal slightly overweight pensioners). I did have excess payload on the rear axle, Rapidos idea was that if I was loaded at the back it would take some weight off the front?? Tried this & in practice didn't. The axle was uprated by fitting new springs & plating to 2000 kgs by SVTECH. Whilst some vans do have a decent payload the makers should be more honest in how it's defined by giving more realistic figures for example a 4 berth van should have the number of people reflected in the overall weight.
There is a failure by the DVLA to accept that motorhomes/caravans are different to commercial vehicles/trailers. Just think about the options it would give manufacturers if we had the limit raised to 4000 kgs, they could actually make a well made 7 metre+ van with decent specifications. As an example the Rapido was well made with the furniture feeling really solid & well made but with lowish payload, compared to the Swift Escape where the furniture felt cheap & flimsy but it had a decent payload.