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

1. Current Condition: The coin has a condition rating of 70 (MBC-), which indicates that it is in relatively good shape. This can positively influence its value.

2. Auction History:
- It has been auctioned 16 times, of which it has sold 15 times. This suggests there is consistent interest in the coin.
- The average hammer price in previous auctions is 51.8 euros, providing a basis for the expected value.
- In past auctions, the hammer price has varied, with a maximum of 180 euros in 2015, although this price may have been influenced by the coin's condition at that time.

3. Starting Price and Estimates:
- The current starting price is 75 euros, which is higher than the average starting price of 38.44 euros. This may indicate that the seller has higher expectations due to the condition or demand.
- The estimated price of 100 euros in a previous auction also suggests there is potential for a higher price.

4. Recent Trends:
- In the most recent auction, the hammer price was 85 euros, indicating that interest in the coin may be increasing.

Based on these factors, an estimated maximum purchase price could be in the range of 85 to 120 euros. This is because the highest hammer price in the past was 180 euros, but considering the current trend and starting price, a price of 100 euros could be a reasonable target, while 120 euros could be the upper limit in case of strong competition in the auction.

Therefore, an estimated maximum purchase price could be 100 euros.