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

1. Starting Price: 100 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 70 (MBC-), indicating that it is in fairly good condition, but not of the highest quality (FDC).
3. Auction History: The coin has been auctioned once in the past but did not sell, which may indicate that interest or demand for this particular coin is not very high.
4. Average Hammer Price: There are no data on previous sales, making it difficult to establish an average hammer price.

Given that the coin has a condition rating of 70 and considering that it did not sell in the previous auction, it is likely that interest in the coin is not very high. However, since the starting price is 100 euros, we could estimate that the maximum purchase price might be in a range close to this price, but not necessarily reaching it.

Taking all these factors into account, an estimated maximum purchase price could be around 80-90 euros. This would allow a potential buyer to consider the condition and auction history without risking paying the full starting price, given that there is no guarantee that the coin will sell this time.