I am looking at a Zabka franchise now.
You don't want to do that under any circumstance.
It was in the media last month - tokfm.pl/Tokfm/7,103090,25731169,ajenci-chcieliby-wyjasnienia-skad-wziely-sie-ich-dlugi-spor.html - essentially, there's some major issue with Żabka forcing promotions on franchisees, but then the franchisees have to pay tax on the non-discounted price. As I understand it, let's say there's a "two hot dogs for 5zł" promotion. You have to run the promotion, but then you pay tax on the basis of having received 8zł (the normal price for two hot dogs) from your customers. It's very strange, but well documented. If you look in a typical shop, you'll see that these promotions are everywhere, so you can see how you end up in a mess tax-wise quickly.
There's also some racket involving the franchisee signing some sort of open-ended credit agreement with Żabka, and when the franchise ends, the franchisee gets hit with huge bills under very unclear circumstances. There are examples where franchisees have kept detailed records showing that they owe nothing, but Żabka presents them with bills for hundreds of thousands of złoty.