To estimate a maximum purchase price for the coin in question, we can analyze the provided data, including auction history and conservation conditions.

1. Current Conservation: The coin has a conservation grade of 70 (VF-), indicating a medium state of preservation. This is important because the price of coins usually increases with better conservation.

2. Price History:
- The average hammer price in previous auctions is 409.17 euros.
- The last auction with a similar conservation grade (70) had a hammer price of 300 euros.
- In previous auctions, hammer prices for coins with a conservation grade of 70 have varied, but they have generally sold between 220 and 380 euros.

3. Starting Price: The current starting price is 300 euros, which is a reasonable starting point.

4. Auction Trends: The coin has been auctioned 13 times, of which 12 have sold. This indicates good demand and consistent interest in the coin.

5. Maximum Price Estimate: Given that the average hammer price is 409.17 euros and considering that the conservation is 70, a maximum purchase price could be set in a range that reflects both demand and conservation.

Taking all these factors into account, an estimated maximum purchase price could be approximately 400 euros. This is based on the price history, current conservation, and trends from previous auctions.