Its called a scale and a hacksaw.
Ha...I hope you collect the dust
Why do you think coins have a milled edge...?
To prevent miscreants from shaving slices off the edge of the coin
In any case (no pun intended) gold coins are sealed in a plastic case,
The coin shop has a device that checks purity without breaking the seal,
Also to be clear,,,there are coins that have a premium because of their history....like a Queen Victoria gold medal...it may be a one ounce of gold but is a collectors item and is worth much more....