To estimate a maximum purchase price for the coin in question, we can analyze the provided data, including the current grade, previous auction prices, and auction trends.

1. Current Grade: The coin has a grade of 75 (MBC), indicating that it is in fairly good condition.

2. Previous Auction Prices:
- In previous auctions, the hammer prices have varied, but there are some relevant data points:
- In 2021, a coin with a grade of 80 sold for 15 euros.
- In 2021, a coin with a grade of 75 sold for 20 euros.
- In 2023, a coin with a grade of 75 sold for 15 euros.
- The trend shows that coins with similar grades have reached hammer prices between 15 and 20 euros.

3. Average Hammer Price: The average hammer price for this coin is 11.71 euros, suggesting that, in general, buyers are willing to pay around this price.

4. Starting Price: The starting price is 10 euros, which is a good starting point for the auction.

5. Auction Trends: The coin has been auctioned 12 times, of which 8 have been sold. This indicates a consistent interest in the coin.

Based on these factors, an estimated maximum purchase price could be between 15 and 20 euros, considering the current grade and previous hammer prices. Given that the grade is 75, a reasonable maximum purchase price could be 20 euros.