Should people ask before patting/approaching your dog?

I have a miniature dachshund so obviously when I take him out, he gets a lot of attention. We have had a lot of situations where people will speed walk over to pat him or to even try pick him up (in which I promptly intervened on). I’ve even had it where we were at a outdoor home hardwear store and he was in the trolley ( it’s a shop dogs are allowed whilst on leads or in trolleys), me and my partner were the only ones in the aisle, we were looking at the shelves for probably 30 secs and look back and there’s a couple patting him. Now he is a good boy so we have no concerns about him being a danger to anyone. But I was always raised with my parents telling me to “always ask the owners before patting a dog, it’s polite and safer”. I always thought it was common curtesy to check with the owner?