I thought I'd give you my dialogue for surviving going to ice cream with the kids and actually eating something. I have done this about four times at three different scoop shops and it works GREAT and I've never had a problem at all. You can read the allergens right on the counter, or go online and read all ingredients before you go in. My husband sometimes calls them to make sure they have my favorite flavors that I can eat before we go in (we can always go to a self serve yogurt place instead).
B&R EMPLOYEE: What can I get for you?
ME: I'll have chocolate fudge in a cup. But, I'm allergic to lots of stuff besides chocolate fudge. So, it would be really awesome if you could help me out so I don't have an allergic reaction. It's really easy, don't worry. If you could first wash off the scoop for me using the sink instead of the bucket. Then scoop a scoop in an area that has never been scooped and put that in a cup for my son. Then, scoop a second scoop from the exact same spot and put it in a cup for me. That would be so perfect. I would love that.
B&R EMPLOYEE: Sure, no problem.
------2 minutes later------------- (I watch him/ her rinse the scoop under the faucet and do 2 scoops in a row)
B&R EMPLOYEE: Okay, this scoop is for your son, this one is for you! ( big smile)
ME: You are the best ever. (leaving tip in tip jar)
If you don't have a kid, you can ask them to scoop a scoop and set it aside to get down to the virgin ice cream level.