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

1. Starting Price: 1200 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 75 (MBC), indicating that it is in fairly good shape, but not the best possible condition.
3. Historical Data:
- It has been auctioned in the past 2 times, of which it sold 1 time and did not sell 1 time.
- The average starting price in previous auctions was 750 euros, and the average hammer price was 300 euros.
- In the most recent auction, the coin was offered with a starting price of 300 euros and sold for 300 euros, with a condition rating of 70.

Given that the current starting price is significantly higher than the previous average hammer price and the starting price of the most recent auction, this suggests that the market may be valuing this coin differently this time.

However, since the condition is good but not excellent, and considering the historical prices, an estimated maximum purchase price could be in a range that reflects both the quality of the coin and the market trend.

Taking all these factors into account, an estimated maximum purchase price could be around 600 to 800 euros. This is based on the fact that, although the starting price is 1200 euros, the sales history and average hammer price suggest that buyers may not be willing to pay that much.