Larry is right on the money. Tire pressure, like wheel alignment is a chassis tuning parameter. For the US, DB tends to recommend minimum pressures for ride comfort, but better handling, reduced fuel consumption and tire wear can be obtained by running pressures in the thrities, and since most Mercs are front heavy with just one or two people aboard, they will respond favorably to biasing the front pressure higher than the rear. This will improve steering response and reduce understeer.
Like most rear drive cars, the tires tend to wear faster on the shoulders at the front and faster in the center at the rear, so regular tire rotations - say at 7500 mile intervals - will tend to even out the wear.