Let's see, the "initial" service would include -
Check the batteries and cables to make sure nothing has shook loose and they are holding a charge properly
Check for fuel, water and oil leaks at all hoses, gaskets etc
Check the starting and idle condition of each motor
Change the engine oil
Inspect the water separating filters
Replace the 10 micron fuel filters
Replace the gear oil
Lubricate all the lube points
Inspect the power trim/tilt
Inspect the sparkplugs
Check the water inlet and check the waterpump for proper operation
Check the wireharness and gauges
With the retail price of a pair of 300's in the 40-50 thousand dollar range, 1000 bucks for service, as a percentage basis of initial cost is actually very cheap in comparison to most outboards.
Even at that cost I would have the check done by an authorized dealer - I personally wouldn't want to take chances should you require a warranty claim down the road - because if they don't check it they could point the finger at you if something goes wrong...