How cheeky is cheeky?

Interested in buying a house and it's currently up for £223k. The estate agent recommended it to us and said the seller was open to offers. Whilst we were at the viewing a different estate agent (but with the same firm) suggested that it's not priced correctly and that's why it's been up for 6 months.

We then received a phone call from the agent asking for feedback the next day, and they said if we were slightly interested or considering putting in an offer to make sure it's cheeky. We were considering offering £205k (approx 8% below asking) but didn't know if that was too low? We've been told that there's been no offers at all so far. We would be first time buyers.