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

1. Current Condition: The coin has a condition of 70 (VF-), indicating that it is in fairly good shape, but not of the highest quality.

2. Auction History:
- The average hammer price in previous auctions is 74.14 euros.
- The coin has been auctioned 9 times, of which it has sold 7 times, indicating good demand.
- Previous hammer prices varied, but there is a notable price of 110 euros in an auction with a condition of 85, suggesting that the price could increase significantly with better condition.

3. Starting Price and Estimates:
- The current starting price is 18 euros, which is relatively low compared to the average hammer price.
- The average starting price in previous auctions is 50 euros, suggesting that the current starting price could be a good opportunity.

4. Price Trends:
- In previous auctions, hammer prices have varied considerably, but the range seems to be between 26 and 110 euros, depending on the condition.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 90 euros, considering that the current condition is 70 and the average hammer price is 74.14 euros. This also takes into account that the starting price is low, which could attract more bidders and potentially raise the hammer price.

Therefore, a reasonable maximum purchase price could be 85 euros.