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

1. Current Condition: The coin has a condition rating of 70 (VF-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- The coin has been auctioned 7 times and has sold on all occasions, indicating a consistent interest in the coin.
- The average hammer price in previous auctions is 410.83 euros, suggesting that buyers are willing to pay close to this price.

3. Previous Prices:
- In past auctions, the hammer price has varied, but it has reached up to 420 euros on several occasions for coins with a condition rating of 85, which is significantly better than the current condition of 70.
- The current starting price is 350 euros, which is reasonable given the price history.

4. Price Trends:
- The average starting price has been 291 euros, but the hammer price has consistently been higher, indicating that buyers are willing to pay more than the starting price.

Given all this, an estimated maximum purchase price could be around 400-450 euros. This is based on the hammer price history and the demonstrated interest in previous auctions, taking into account that the current condition is lower than that of coins that have reached higher prices.

Therefore, a reasonable maximum purchase price could be approximately 420 euros.