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

1. Starting Price: 900 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 70 (VF-), indicating that it is in fairly good shape, although not the best possible condition. This may influence collectors' interest.
3. Auction History: The coin has been auctioned once in the past but did not sell, which may indicate that the starting price is high or that there is insufficient demand.
4. Average Hammer Price: There is no data on previous sales, making it more difficult to estimate a hammer price.

Given that the starting price is 900 euros and considering that it did not sell in the previous auction, it is possible that bidders may be willing to offer a bit less than the starting price. However, since the condition is reasonably good, we could estimate that the hammer price might be close to the starting price but not necessarily reach it.

Taking these factors into account, an estimated maximum purchase price could be between 700 and 850 euros. This would allow bidders to have a margin to compete without reaching the starting price, which could be considered high if there is not enough interest.