To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Condition: The coin has a condition of 70 (VF-), indicating that it is in relatively good shape. This suggests that its value might be closer to the auction prices of coins with similar conditions.

2. Auction History:
- Previous auction prices for coins with similar conditions (like 80) have reached up to 30 euros (in 2018) and 16 euros (in 2021).
- The average auction price in the past has been 15.67 euros, which is also a good indicator.

3. Starting Price and Average Starting Price: The current starting price is 10 euros, and the average starting price in the past has been 12.75 euros. This suggests that the starting price is reasonable and could attract bidders.

4. Sales Trends: The coin has sold in 7 out of the 10 times it has been auctioned, indicating a consistent interest in the coin.

5. Price Estimation: Given that the condition is good and considering previous auction prices, an estimated maximum purchase price could be between 20 and 30 euros. This is based on the fact that the current condition is better than some of the coins that have sold in the past for higher prices.

Therefore, an estimated maximum purchase price for this coin could be 25 euros. This reflects a balance between the condition, price history, and interest in the coin.