It says it right on the bar: 'fine gold'.
LOL but if i was a noob and i was buying it, who would i trust? how would i check quickly for myself

Here is a way:
You weigh it (on an accurate scale), than you measure the volume by putting it into a finely graded measuring cylinder with some water. Note the increase in volume when adding the gold bar. The volume for one kg gold should be 51.86 cubic centimeters (ml).
This method is easily defeated with gold-coated tungsten alloy. Like I said, portable XRF.
Edit: damn it justusranvier, you're quick on the trigger
