Though altering incomming is one thing, the outgoing another?

If a player collects a coin, it tells the database it found 1 coin. The next time a player logs in it retrieves the amount of coins for the player, and it returns 1. The player can then alter this to be 1000, but the database still has it registered as 1.

The incomming connection is not so important as the outgoing. Is the outgoing query just as easy to manipulate?