Moo,
Yes and No.
Most of the time laws are followed and karat gold is marked within a reasonable percentage of gold content, but crooks do not always follow the rules, so testing is the only way to be sure the mark is not stamped on a item which it should not have, every once in a while you can find karat gold unmarked, although seldom it does occur, again testing will tell you what you have.
Some high gold content material will not have marks or stamps, like dental gold, here testing can help, but with dental gold it is sometimes hard to tell because it can contain other metals resistant to acids we test with sometimes these other metals are also valuable like the PGM's, sometimes these other metals are not that valuable.
Keep your promise to your self and keep reading Hoke's book it is your best bet to becoming successful.
She also wrote a book on testing metals, and pawnbrokers Bobs guide is also a very good document on how to test, there is a recent post in the book section with links to both of these.