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

1. Current Condition: The coin has a condition of 75 (MBC), indicating that it is in fairly good shape, although not the best possible condition.

2. Auction History:
- It has been auctioned 3 times in the past and has sold on all occasions.
- The average hammer price in previous auctions is 34 euros, with an estimated price of 30 euros in one of the auctions.

3. Starting Price: The starting price is 10 euros, suggesting that there is considerable room for the hammer price to be higher.

Given that the current condition is lower than that of the auction where it sold for 34 euros, and considering that the average hammer price is 34 euros, we could estimate that the maximum purchase price could be in a similar range, but adjusted for condition.

A reasonable approach would be to consider a discount on the previous hammer price due to the lower condition. We could estimate a maximum purchase price around 25-30 euros, taking into account that condition is an important factor and that the previous hammer price was 34 euros.

Therefore, an estimated maximum purchase price could be 30 euros.