Do you have to waste your time doing the Sudoku before you find out it's flawed?

I do a ton of them, and I have never found one published in the paper that was flawed. Friends have shown me ones they thought were bad, and I showed them their mistakes.

My sister and I both enjoy Sudoku. I’m not as fast as she is, particularly on the difficult levels, which is why they are done in pencil. If it fails, the marks are erased and I start over at a later point. They all eventually work out, and I’m one who checks my work.

What is the source of the puzzles you are using?

I’ve never come across a flawed one. It must be one in a million that there is a flaw.

But what is the method of verifying it?
@Pied_Pfeffer I’m not doing the puzzle. I don’t do it that often.
This question came from someone whose time is super, super valuable (so that’s not me). Even if it happens once in gizillion times, how to verify it.

The Sudoku puzzles that I have done are from a book, the newspaper, or a website. All have provided a source where, if the puzzle doesn’t work out by user, an answer source is provided.

I mean verifying it for flaw before starting to do the puzzle. Like there shouldn’t be two of the same digit in the same box or line, which is easy enough to spot. Not all flaws are easy to spot.

There is no way to verify a Sudoku flaw without testing it first. This is the responsibility of the publisher.

@Pied_Pfeffer I suppose so it is the responsibility of the publisher.
This link could be about that.
http://forum.enjoysudoku.com/samurai-flawed-t1079.html
or http://tinyurl.com/ocy5vqe