My family recently purchased a 1873 Italian Gold 20 Lira from eBay, with the listed weight as 6.45 grams. Since acquiring some precision electronic scales we find the coin only weighs 6.15 grams, 0.3 grams underweight, or about 5% under. Does this mean the coin is definitely a fake? Or is there a chance it's just naturally low, mint error perhaps.
What condition is the coin in? Are there any gauges out of the coin? Knapping could be a reason for an underweight coin? Any chance on seeing a picture?