The difference between supermarket produce (fruit/veg) and greengrocer produce is night and day IMO.
As for carrots specifically, I did notice that the greengrocer carrots often are individually smaller and more fucked up looking than the supermarket ones, and taste more intensely.
Interestingly the greengrocer is often cheaper on some things than even the discounter supermarkets, and is MUCH cheaper if you factor in spoilage, disposal of packaging waste, etc.
Same goes for meat products - buying them from a good butchers can often work out cheaper than the supermarket (precise control over cuts, etc), far less waste, professional advice on preparation, higher quality, etc.
Waitrose sell some very nice tomatoes, albeit at very premium prices.
Sainsbury’s often stock UK-grown Thanet Earth tomatoes (look for “jubilee vine tomatoes” etc) which are some of the best I have found at normal prices, especially out of season.
I'm worried that modern carrots are lacking in nutrition due to being heavily selected for size and colour.