To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition rating of 30 (BC+), indicating that it is not in very good shape. This generally reduces its value compared to coins in better condition.

2. Historical Prices:
- The average hammer price in previous auctions is 402.78 euros, suggesting that, in general, buyers are willing to pay significantly higher prices than the starting price.
- However, the hammer prices for coins with a similar condition (30) have been lower. For example, in previous auctions, the hammer price for coins with a condition of 30 was 120 euros and 170 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 150 euros, which is below the average starting price of 175.5 euros. This could indicate that the seller is looking for a quick sale or that the coin does not have great interest in the market.

4. Sales Trends: The coin has been auctioned 12 times, of which it has sold 9 times. This suggests that there is consistent interest in the coin, although the fact that there are 3 occasions when it did not sell may indicate that the starting price has not always been attractive.

5. Maximum Price Estimate: Given that the condition is low and considering previous hammer prices, a reasonable maximum purchase price could be in the range of 150 to 200 euros. This is based on the fact that buyers may be willing to pay a little more than the starting price, but not enough to exceed the hammer prices of coins in better condition.

Maximum Purchase Price Estimate: 200 euros.