They never finished a job properly (not even once).
It's called inversion
Inversion not only can be used to form questions and conditional sentences. Also, we can use inversion for emphasis.
* Little did she know how much work was left.
* On no account must you sleep at school.
* Never should you remember who's your boss.
* Only then can you belong to me.
* Here comes the sun.
All these structure are rather literary, which means there are more likely to appear in books.
More informantion here:
Inversion of the verb after certain adverbs
- For Teachers