At Bullion DIrect right now, a 10 oz bar has a bid of $146 and an ask of $160. And the $146 is delivered to them, so that means he would net a little less, since he pays for shipping. He can use a flat rate box, and net about $135.
So, it would net him $135, and cost you $160. I'd split the difference with the guy. With ANY guy - or gal. And offer $145. Just me.
You are getting a deal, and he is getting a deal.
If you want more of a deal, I wouldn't go below $135. Otherwise hard feelings could come up in the future.