To estimate a maximum purchase price for the coin in question, let's consider the following factors:

1. Starting price: 75 euros.
2. Average hammer price in previous auctions: 81.5 euros.
3. Current condition: 10 (good), which is a fairly low condition.
4. Auction history: It has been auctioned 2 times and sold on both occasions, indicating interest in the coin.

Given that the condition is low (10), the hammer price may not be as high as the average of 81.5 euros. However, the interest in the coin and the fact that it has sold in the past suggests there could be additional value.

Based on the previous average hammer price (83 euros) and considering the current condition, an estimated maximum purchase price could be between 70 and 80 euros. This is because, although the starting price is 75 euros, the condition may limit buyer interest.

Therefore, an estimated maximum purchase price could be 75 euros. This aligns with the starting price and reflects the condition of the coin.