A It is one of those dilemmas that depends so much on the circumstances. Turning away an aggressive customer can be stressful enough in its own right, and in some cases the situation could turn even nastier if you're attempting to seize property from them.
But police and Trading Standards officers appreciate it when retailers present them with fake ID cards. Not only does it help them form a better picture of the tactics of under-age drinkers, it also demonstrates to them that you take your responsibilities seriously.
If you think an ID card is fake, and that you're not at risk of violence, politely inform the customer that you have concerns about the card and you think the matter needs to be taken up with the police. Tell them they can come and collect it the following day, and if the card proves to be genuine they will receive an apology. Chances are you will not see the customer again.