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

1. Coin Condition: The coin has a condition rating of 75 (MBC), indicating that it is in fairly good shape, but not of the highest quality (FDC).

2. Historical Auction Data:
- The average hammer price for similar coins has been 51.7 euros.
- In previous auctions, coins with a similar condition (around 75) have had hammer prices that varied, but some examples are:
- A hammer price of 40 euros for a coin with a condition of 85.
- A hammer price of 35 euros for a coin with a condition of 80.
- A hammer price of 20 euros for a coin with a condition of 30.

3. Starting Price and Estimates:
- The current starting price is 20 euros, and the average starting price for similar coins is 36.6 euros.
- The estimated price for this coin is 50 euros.

4. Sales Trends: The coin has been auctioned 177 times, with an 81% sell-through rate (143 times sold). This suggests there is consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 50 to 70 euros, considering that the average hammer price is 51.7 euros and that the coin's condition is good. However, since the starting price is 20 euros, it is likely that buyers will be willing to pay a little more, but not excessively, given that the condition is not the highest.

Therefore, a reasonable maximum purchase price could be between 60 and 70 euros.