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

1. Starting price: 1400 euros, which is the initial price of the auction.
2. Current condition: 70 (MBC-), which is lower than the condition of 80 from the previous auction. This could indicate that the value of the coin may be less than in the previous auction.
3. Previous average hammer price: 1200 euros, which is the price at which the coin was sold in the previous auction.
4. Demand: The coin has sold in the past and there have been no failed sale attempts, suggesting that there is interest in the coin.

Given that the current condition is lower than that of the previous auction and the average hammer price was 1200 euros, an estimated maximum purchase price could be slightly below this value, considering that condition affects the price.

Therefore, an estimated maximum purchase price could be around 1100 to 1150 euros. This takes into account the condition and the previous average hammer price, as well as the interest in the coin.