Let us know how it goes.
Perhaps you could track that listing and see what (and if) it eventually sells at. That would be a good reference point as to how the market in doing in that neighborhood.
If it were me, I’d have low-balled at $350k. If the seller really thinks that his house is worth $450k, let him sell it to someone else at that price and have the last laugh. Why get insulted if you know you’ll have money in the bank? The sellers who get insulted by a low-ball offers are the desperate ones.