Frauds using stolen card usually are only able to use it a few times before it gets cancelled.
So they tend to go for high value items.
If it is a sale that is "too good to be true"
It could well be fraud and needs further investigation before dispatch.
A phone call to the "customer" is a start but doesn't guarantee its valid particularly with mobiles.
You could verify that the customer has access to the card.
(I am not sure if authorize.net can do this)
Manually charge them a few cents, (remove their email address so they don't get a copy of the transaction)
Email the customer, tell them you need to verify their card.
Have them email you the amount you have just charged them
If they do confirm the correct amount, then they have full access to the card, so it should be valid (refund the few cents you charged them)
Someone who has stolen the card won't be able to confirm this amount. So refund the sale and the few cents extra, and cancel the order as its fraud.
If you are still suspicious refund the card and request a "Direct Bank Transfer" to your Bank Account.
This may "annoy" a few customers, but if they want the coin they will probably do it.