I inherited a system that let you put AAA in the product price field and would persist it. Validation is hard to get right so they simply didn’t try, not even

I inherited a system that let you put AAA in the product price field and would persist it. Validation is hard to get right so they simply didn’t try, not even common sense. I’ve spent years thinking about the optimal way to structure validation and I’ve never come up with an approach I really like on an architectural level so I do the usual approach of simple sanity checks on the client and proper validation against business logic on the server but even that isn’t as isolated as I’d like.