To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current starting price: 350 euros.
2. Coin condition: 70 (VG-), indicating a medium-low condition.
3. Auction history:
- The coin has been auctioned 9 times and has sold on all occasions.
- The average hammer price in previous auctions is 342.63 euros.
- Previous hammer prices for coins with similar condition (70) have varied, with the highest being 420 euros in a recent auction.

4. Price trends:
- In previous auctions, the hammer price has ranged from 201 to 480 euros, with an average of 342.63 euros.
- The last auction with a hammer price of 420 euros suggests that there is growing interest in this coin.

Given that the coin has a condition of 70 and considering the price history, an estimated maximum purchase price could be around 420 euros, which is the highest recorded price for coins of similar condition in recent auctions. However, since the starting price is 350 euros, it is reasonable to consider that the hammer price could be close to this value but not exceed 420 euros.

Maximum purchase estimate: 420 euros.