Is my new GM3 up to par?

[messyhousedesign]

Hi everyone!,
After winning a bid on ebay I'm going to receive my new/used GM3 soon. The seller seems to be a reputable seller, so I shouldn't have any problems returning it if anything is wrong. But that is the problem, I will not know if something is "wrong". So my question is, can anyone spare some tips on testing if functionality and accuracy is up to par? This will be my first nugget detector, but I have downloaded and read the manual through and through so I have a basic understanding of how this machine is supposed to work.

p.s. Its comes with a new DD coil and also a 1.5 grain nugget attached to a poker chip for tuning.