a supermarket would not have to pay for neutering nor the removal as feral cat collines and wild dogs coe under the marie. They may however have to pay for a professional to come and trap them which could be claimed off insurance.
while its great you have saved a few its impossible for a supermarket to keep cats same as a restaurant imagine going to a restaurant to find it full of cats in the kitchen cats in the dining area. while Ratatouille was a brilliant movie Catatouille in real life would just not be accepted. Plus the damage the cats would do to such huge numbers of stock would be very costly and in turn bring in other rodents in high numbers.
Supermarkets when invaded by such high numbers or even low numbers ,that to call in someone to trap them is a sad fact and its unfortunate that a great number of them unless an association can be found to take on the financial burden of them could be found would be put to sleep but not at the supermarkets expense.
I’m sorry you had no help but that is 100% down to your marie who’s responsibility it falls down to for wild dogs and feral cats. most maris have an agreement with places and fouriers.