This is a fun question. Can I look at the coin's two sides? If not...I assume you now have to start applying statistical tests (given that a fair coin will only do this once out of 1024 times, what are the chances I've got one of those 999 coins vs the 1/1000 chance that I picked the double headed coin?) or is there some simplifying assumption I'm missing.
Anyway--assume I think all that aloud in an interview. What does that tell you about the candidate?
I would give points for just asking that question, because many people bound by conventional thinking wouldn't dare to ask it, accepting default assumption that you can't. I'm not saying this says anything about your ability to solve the problem, but asking the question is a good sign of a supple mind.
You can only see the result of the flips, you can't examine the coin. Yes, it comes down to estimating the probability of having a biased coin given that you have seen it come up heads ten times in a row.
Anyway--assume I think all that aloud in an interview. What does that tell you about the candidate?