What are your main concerns when interviewing candidates for a copywriting position?

I believe to give the assignment practically to see the below point which is very important for      the position of copywriter

A -Mistakes. Misspelled words or grammatical errors should be avoided.

B- Style. A writing style wildly inconsistent with your needs.

        C-Can meet deadlines. If a writer can’t meet a deadline, that is best candidate.

I will consider an inquisitive writer who conducts back grounding and research before submitting any work , I may ask him how would you describe our brand’s tone / voice , also I may ask him who he thinks our target audience are !

A good copy writer should possess the below skills

1) Mistake free writing

2) Creativity

3) good Intellectual

4) General Knowledge

5) Effective (Deadline maintaining)

The level of observing details, i may do this by asking him to describe something for me ( maybe a pen ) or by open a conversation about specific product.

I, personally, believe that the right candidate should show the ability of thinking out of the box, the ability of communicating with the target people in the right way.

Also, he/she has to possess a good knowledge of local norms and  cultural practices.

I think

the speed of writing and focusing

I agree with all answers thanks for invitation 

his\\her command of English skill and the most important  to be visionary and creative in some way 

Translation ability, you don't want to hire someone can write one language, must be both and ability to translate, so that's the first, second is the speed of writing,3rd is the skills of writing, and finally the most important thing the personality, seen they have no problem working under pressure, so a test should be in place.

My top consideration is creativity ...