That sucks you were treated that way OP! I can see the reasoning on the non approved free cereal, but not when you exchanged for approved cereal. Personally, I would have just left at that point and came back when I had more tine and when the store manager would be there.
However, even though you were treated badly, I don't quite understand why they couldn't have been at least notified that juice had been spilled. Someone can slip and get pretty hurt ( I've broken my foot slipping on something slippery before and its not fun).
Two wrongs don't make a right sorta thing iykwim...