[username90]

If you do hire them but your process can't tell the difference between them and the bad engineer they work with they will get frustrated and quit soon. The most important part to keep good engineers is to ensure they don't have to work alongside bad engineers.

[AlchemistCamp]

I can't imagine a situation where I couldn't tell the difference between either of them and a bad engineer. I'd either be pair programming with them and learning a lot or be pairing with a "bad engineer" and suffering.

[Viliam1234]

Sometimes people making the decision about hiring are not programmers themselves, or happen to be the bad engineers. In both cases, the difference between a good and bad engineer can be invisible for them.