Possibly, but the point is, you really need to be able to test some things yourself, assuming you plan to have the tank running long term. There is SO MUCH MORE that happens in a new tank than just the initial nitrogen cycle.
As for the test the store uses, here is my thinking:
1. The test may or may not be reliable
2. The person doing the test may or may not run it correctly
3. Different people might do the test each time
4. If you do your own testing, even if your procedure is off a little, you likely will follow the same process each time so your test results will still tell you if something is increasing or decreasing.
Plus, in an emergency, it's always good to be able to test the water yourself rather than have to wait until the fish store is open.