Based on the data provided, we can observe that the coin in question has had an average auction closing price of 270.93 euros in previous auctions. Additionally, its condition has been maintained at an average of 85 (ebc-).

Considering that the coin will be auctioned in the coming days with a starting price of 400 euros, we can estimate a maximum purchase price based on the historical average auction closing price and the condition of the coin. Given that the condition is good (85), and considering that the average auction closing price has been 270.93 euros, we could consider a maximum purchase price around 300-320 euros.

It is important to note that the final auction price may vary depending on the demand at that specific moment, so it is advisable to pay attention to the auction to adjust the offer accordingly.