To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Condition: The coin has a condition rating of 95 (S/C-), indicating that it is in very good shape. This generally increases its value compared to coins with lower conditions.

2. Auction History:
- The average hammer price in previous auctions is 39.4 euros, suggesting that, in general, buyers are willing to pay significantly more than the starting price.
- In the 2018 auction, the coin was sold for 130 euros, which is an exceptionally high price and could be an outlier, but it indicates that there is potential for high value in the market.

3. Starting and Hammer Prices:
- The current starting price is 12 euros, and the average hammer price in previous auctions is 39.4 euros. This suggests that the hammer price could be in a higher range than the starting price.

4. Auction Trends: Since the coin has been sold on all previous occasions and there have been no failed attempts at sale, this indicates a steady demand.

Based on these factors, an estimated maximum purchase price could be in the range of 40 to 60 euros, considering that the average hammer price is 39.4 euros and that the coin's condition is high. However, taking into account the exceptional hammer price of 130 euros in 2018, it might be reasonable to consider a maximum price of up to 70 euros, depending on the competition in the auction and the interest of collectors.

Therefore, an estimated maximum purchase price could be 60 euros.