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-). This indicates that it is in an acceptable state, but not of high quality.

2. Historical Prices: By looking at the auction prices of coins with a similar condition (70), we can see that they have varied. For example:
- In 2020, a coin with a condition of 70 was auctioned for 60 euros.
- In 2019, another coin with the same condition sold for 36 euros.
- In 2021, a coin with a condition of 70 was auctioned for 30 euros.

3. Average Auction Price: The average auction price for this particular coin is 170.89 euros, but this includes coins of different conditions. Given that the condition of the coin in question is 70, it is likely that the actual auction price will be lower than this average.

4. Starting Price: The starting price is 18 euros, which indicates that the auctioneer expects moderate interest in the coin.

5. Market Trends: The coin has been auctioned 103 times, with a high percentage of sales (92 out of 103). This suggests that there is an active market for this coin.

Based on these factors, an estimated maximum purchase price for the coin could be between 50 and 80 euros, considering that it is a coin in VF- condition and that previous auction prices for similar conditions have been in that range.

Therefore, a reasonable maximum purchase price could be 70 euros.