To estimate a maximum purchase price for the coin that will be auctioned, we will consider several factors:

1. Condition of the coin: The coin in question has a condition rating of 75 (MBC). This indicates that it is in a medium-low state of preservation, which will affect its value compared to coins in better condition.

2. Previous auction prices: By observing the hammer prices of coins with similar conditions, we can see that prices vary. For example, in previous auctions, coins with conditions ranging from 80 to 90 have reached hammer prices between 40 and 300 euros, depending on demand and rarity.

3. Average hammer price: The average hammer price for this particular coin is 99.9 euros, suggesting that, in general, buyers are willing to pay close to this amount.

4. Starting price: The starting price is 18 euros, indicating that there is considerable room for the hammer price to be higher.

5. Market trends: Since it has been auctioned 1260 times and sold 955 times, there is good demand for this coin, which may increase its price at auction.

Taking all these factors into account, an estimated maximum purchase price for the coin in question could be between 80 and 120 euros, considering its condition and previous hammer prices. However, since the average hammer price is 99.9 euros, a reasonable maximum purchase price could be approximately 100 euros.