To estimate a maximum purchase price for the coin that will be auctioned, we can analyze the provided data:

1. Starting price: 175 euros.
2. Condition of the coin: 70 (MBC-), indicating an average condition.
3. Previous hammer prices: Previous hammer prices have varied, but there are some relevant data:
- In previous auctions with similar conditions (for example, 80 and 85), the hammer prices were 260 euros and 560 euros, respectively.
- The average hammer price in the past has been 257.56 euros.

4. Auction trends: The coin has been auctioned 11 times, of which it has sold 9 times. This indicates a consistent interest in the coin.

5. Average starting price: 156.25 euros, suggesting that the current starting price (175 euros) is slightly higher than the average, but not excessively so.

Given that the condition of the coin is 70 (MBC-), and considering the hammer prices of coins with similar conditions, an estimated maximum purchase price could be situated between the starting price and the average hammer price.

Estimated maximum purchase price:
We could consider a range between 250 and 300 euros, based on the average hammer price and the trend of previous auctions. A reasonable maximum price could be 280 euros. This is based on the expectation that the coin could reach a hammer price similar to that of previous auctions with comparable conditions.