Hi Inga,
In the Maresme you should still have negotiating power, especially if the property has been on the market for 6 months already, means it’s not a bargain in hot demand. Maybe offer 15% less and aim for 10%. What does the agent recommend? It’s not yet a vendor’s market so an offer of 85% should be taken seriously. And if it hasn’t sold in 6 months it sounds like it’s not priced to sell. How does the asking price compared to similar properties in the area?