Should you believe an archaeologist that claims he found some gold coins dated 46BC?
This would depend on how they dated it and where they found it.
Although it was not common, gold coinage was in use at this time so as long as the interpretation was based on good evidence there is no reason not to believe them.
If the coin was dated by an inscription saying "46bc"
then you have a not very convincing archaeologist and a fake coin.
No one before Christ's birth would have known the date or time of
his birth; therefore they would not have been able to date a coin
46 years before his birth.
The archaeologist was telling a lie as a coin can not be dated in BC as no one at that time would be knowing that Jesus Christ was to take birth in future.