To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

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

2. Auction History:
- The average hammer price for this coin in the past is 13.89 euros.
- In previous auctions, hammer prices have varied, but some relevant examples are:
- In 2021, a coin with a condition of 95 was sold for 12 euros.
- In 2022, a coin with a condition of 100 was sold for 20 euros.
- In 2022, another coin with a condition of 95 was sold for 20 euros.

3. Starting Price and Estimates:
- The current starting price is 9 euros, and the average starting price is 8.69 euros. This suggests that the starting price is reasonable compared to the history.

4. Price Trends: Given that the coin is in good condition and has had hammer prices reaching up to 20 euros in the past, it is reasonable to assume that the hammer price could be in a similar range.

Based on these factors, an estimated maximum purchase price could be between 15 and 20 euros, considering that the condition is high and there is a price history that supports this estimate. Therefore, a reasonable maximum purchase price could be 20 euros.