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

1. Starting Price: 125 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 20 (BC-), indicating that it is not in very good shape. This may affect its value compared to coins in better condition.
3. Auction History: The coin has been auctioned twice in the past, and on both occasions, it has sold. The highest recorded hammer price was 130 euros, indicating that there is interest in this coin despite its condition.
4. Average Hammer Price: The average hammer price for this coin is 127.5 euros, suggesting that, in general, buyers are willing to pay around this price.

Given that the starting price is 125 euros and considering the sales history and the average hammer price, an estimated maximum purchase price could be slightly above the starting price, but not too much, given the condition.

Therefore, an estimated maximum purchase price could be approximately 135 euros. This takes into account the previous interest in the coin and the fact that the highest hammer price was 130 euros, allowing for a small margin for competition in the auction.