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

1. Current Condition: The coin has a condition of 85 (ebc-), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Current Listing Price and Previous Prices: The current listing price is 1800 euros. The average hammer price in previous auctions is 1892.08 euros, suggesting that similar coins have reached prices close to this value.

3. Historical Trends: By observing previous hammer prices for coins with similar conditions (85 and 90), we can see that they have reached hammer prices that vary but are generally above the current listing price. For example, in the auction on 2022-03-17, a coin with a condition of 90 was hammered at 2800 euros.

4. Demand and Supply: The coin has been auctioned 28 times in the past, with a sell-through rate of 96.4% (27 out of 28). This indicates good demand, which could push the price up.

5. Comparison with Recent Hammer Prices: In recent auctions, hammer prices for coins of similar condition have ranged from 1800 to 2800 euros, suggesting that the hammer price could be in a similar range.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 2200 and 2500 euros. This is based on the condition, the price trend in previous auctions, and the observed demand.