I tend to shop at a huge Asda. We live in the countryside and it is our nearest supermarket.
Since DS was born 19 weeks ago, I guess I have been about 10 times. I always check out the Parent spaces and, so far, have never found one free. So I end up parking at the very far end of the car park where I can find two or three spaces together so I can open the car doors to get DS's car seat out and carry him miles to the shop. A lot of the time there have been cars in the P&C spaces that I suspect are not actually P&S cars (two seaters, sports cars with luggage all over the back seat).
On about half my visits there have not been any of those trolleys that I can put his car seat in either.
I have asked customer services if they could consider adding more P&C spaces or policing the existing ones. They have not been interested and have suggested that I shop at different times of day, although all my vists have been at different times of day! (well morning or afternoon, DS hasn't really got into 24hr shopping yet).
I would shop online, but they won't come to us.
The flip side is that our local economy is thriving as I can't be bothered with the big supermarkets any more. But they are handy for things like cans and breakfast cereal.