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 70 (MS-), indicating that it is in an acceptable state, but not of the highest quality. This may influence the price, as coins in better condition tend to fetch higher prices.

2. Auction History:
- In the past, this coin has been auctioned three times, and all have successfully sold.
- The previous hammer prices are:
- €269 (condition 70)
- €340 (condition 80)
- €400 (condition 85)

3. Average Hammer Price: The average hammer price for the previous auctions is €336.33, which provides a good reference point.

4. Starting Price: The current starting price is €275, which is slightly lower than the average hammer price.

5. Price Trends: Given that the coin has sold successfully in the past and considering that the current condition is 70, it is reasonable to expect that the hammer price will be in a similar range to the previous auctions.

Taking all these factors into account, an estimated maximum purchase price could be around €350-370, as this reflects a moderate increase over the starting price and aligns with the hammer prices of previous coins in similar condition.