When this is the case, are there kashrut concerns with eating the frozen yogurt (without any toppings) in an uncertified storefront? (All the ones I can think of seem implausible: that the yogurt might have been heated to yad soledet bo, that kavush might have occurred, or that the franchisee might have adulterated the yogurt.)
Here are some excerpts from an Alert issues by the CRC (Chicago Rabbinical Council) an April 29th, 2013- [If anyone has a more permanent link, please update it]:
The cRc does NOT certify any Cold Stone store or the bulk pack ice cream that is sold by the scoop from behind the counter in any of these stores. The cRc only certifies specific Cold Stone ice cream flavors that are sold in a retail quart container IN THEIR ORIGINAL SEALED PACKAGES.
The cRc and the OK do NOT certify any Red Mango Frozen Yogurt stores. Red Mango Original Yogurt and Red Mango Classic Yogurt are certified by the OK IN THEIR ORIGINAL SEALED PACKAGES.
In some cases, the scoop must be first washed clean. Any other products purchased, such as cones, toppings, or any other additives must also be inspected to determine if they are kosher. Items such as cakes and novelty items may be coming in from another outside source, so special care must be taken when purchasing any of these items. Since one may not assume that there were no changes made since the last visit, this all must be done each time you go into the store to make a purchase!