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

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

2. Auction History:
- The coin has been auctioned 9 times and has sold on all occasions, suggesting there is consistent interest in this coin.
- The average hammer price in previous auctions is 255 euros, which is a good indicator of market value.

3. Previous Auction Prices:
- Hammer prices have varied, but there are examples of hammer prices exceeding 300 euros, even reaching 550 euros in a previous auction with a condition of 90.
- The last auction with a condition of 75 had a hammer price of 160 euros.

4. Starting Price and Estimates:
- The current starting price is 150 euros, which is reasonable given the price history.
- The estimated hammer price in previous auctions has been higher than the current starting price.

Based on these factors, an estimated maximum purchase price could be in the range of 250 to 300 euros, considering that the current condition is 75 and that interest in the coin appears to be strong. This also takes into account the average hammer price of 255 euros and the fact that higher prices have been reached in previous occasions.

Therefore, a reasonable maximum purchase price could be 280 euros.