I see it as you have two choices: write it all off and start with the accumulation of parts; or send it back and let him back at it. It sounds to me like he might be beyond his comfort zone with your request. So I would question his ability to meet the new goal too. But - you are connected to him via the dollars. IMO he used some parts I wouldn't have used. But everyone has their own recipe. You are asking a lot with that goal. 600 isn't to bad. 700 is harder to keep alive just as Andy said.