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

1. Starting Price: 30 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 70 (VF-), indicating that it is in fairly good shape. This can generally increase its value compared to coins in lower condition.
3. Auction History: The coin has been auctioned once before, with a hammer price of 15 euros. This suggests that, despite a starting price of 30 euros, market interest may not be as high as expected.
4. Average Hammer Price: The average hammer price of 15 euros also indicates that, in general, buyers are willing to pay less than the current starting price.

Given that the coin has a relatively good condition (70) and considering the auction history, an estimated maximum purchase price could be slightly higher than the previous hammer price, but not as high as the current starting price.

Taking all these factors into account, an estimated maximum purchase price could be around 20-25 euros. This reflects moderate interest, given the auction history and the condition of the coin.