CPD: How do you let customers use your computers?

I work in OD CPD. Plenty of customers come in and expect that they can use our computers to access their emails and 'print something they need from there.' Many customers are kinda shocked when I tell them they cannot use our computers for said request ("It's against company policy sir.") and that they must email me what they need printed or hand it over on a flash drive. "What?! But the other place lets me use their computers for printing." they'll huff and puff for a few seconds until I ask, "do you have your smart phone on you?" (I'm not even sure customer has one, but once i ask, they without fail produce one and begin the process of sending me their email)

there's only a couple of reasons i'll turn the screen/keyboard over to the customer:

1. Inputting shipping info
2. DesignIT+
3. Looking up Rewards
4. Turning screen partially to confirm with customer that file on screen is the one they want printed or to confirm scan quality. This is the only one where the customer sees employee side of the desktop with me.

What about your CPD? Tell me; how many terminals do you have? Do your repeat customers already know the jist of how you run things? how much freedoms do your give your customers in your department?