Based on the provided data, we can observe that the coin has had an average starting price of 15 euros and an average selling price of 30.5 euros in previous auctions. Additionally, the current condition of the coin is 70 (VF-).

Considering that the coin has been auctioned 4 times in the past and has been sold on all those occasions, we can assume that there is interest in it.

Given that the starting price this time is 25 euros and taking into account previous prices of 25, 21, and 16 euros in previous auctions, as well as the condition of 70 (VF-), we could estimate a maximum purchase price around 30-35 euros.

Therefore, my estimate for the maximum purchase price for this coin in the next auction would be around 30-35 euros.