To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Starting price: 170 euros.
2. Current condition: 75 (MBC), which is a fairly good condition.
3. Auction history: The coin has been auctioned 2 times in the past and has sold on both occasions. This indicates a consistent interest in the coin.
4. Average hammer price: 210 euros, which is the average price it has sold for in the past.
5. Average starting price: 140 euros, which is lower than the current starting price, suggesting that the current starting price is higher than the historical average.

Given that the condition of the coin is good (75) and considering the average hammer price of 210 euros, an estimated maximum purchase price could be in a range that reflects both the condition and the interest in the coin.

Taking all these factors into account, an estimated maximum purchase price could be approximately 200-220 euros. This is based on the average hammer price and the good condition of the coin, suggesting it could reach a price similar to or slightly above the historical average.