Based on the provided data, we can observe that the coin is in a conservation grade of 30 (BC+), indicating that it is not in poor condition but also not in excellent condition.

Historically, the coin has been auctioned four times before, with starting prices ranging from 12 to 200 euros. The average starting price has been 50.2 euros, while the average final price has been 100 euros.

In previous auctions, the estimated price of the coin has ranged from 20 to 350 euros, with final prices mostly aligning with the estimates in most cases.

Given that the coin will be auctioned soon with a starting price of 12 euros and considering the previous prices and the current conservation, we could estimate a maximum purchase price around 30-40 euros. This estimation is based on the trend of previous prices and the fact that the coin is not in exceptional condition.