To estimate a maximum purchase price for the coin that will be auctioned, we can consider several factors:

1. Coin Condition: The coin has a condition rating of 95 (S/C-), indicating that it is in very good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Starting Price: The starting price is 400 euros. This is a good indicator of the value that the seller expects to obtain.

3. Auction History:
- The average hammer price in previous auctions is 84.45 euros, but this may not be representative due to differences in the condition of the coins.
- In past auctions, we have seen hammer prices that vary significantly, with some reaching up to 850 euros in a recent auction for a coin of similar condition (95).

4. Price Trends: In previous auctions, coins with conditions ranging from 85 to 95 have had hammer prices ranging from 120 to 850 euros, depending on demand and other market factors.

Given that the coin in question has a high condition rating and a starting price of 400 euros, an estimated maximum purchase price could be set in a higher range than the starting price, considering the possibility that collectors may be willing to pay more for a coin in such good condition.

Estimated Maximum Purchase Price: It could be reasonable to estimate a maximum purchase price between 600 and 800 euros, depending on the competition in the auction and the interest of collectors.