It's not been agreed no that's what if offered him tonite n he's turned it down wanting a third,
Ok. I'm tired so my figures may not quite add up
So you have offered him £70 before tax (rounded up from £69.24) per day. I've based this on 5 days a week 52 weeks per year. (you need to take his hols into account here aswell)
Over 5 days you would like him to bring into the business £260 per day.
That is your stumbling block, it's too ambitious for one person. Or maybe you work together to bring £260 in? If so £18k is about right.
I would have a good think tonight about it.
IF he is the person to take you forward what have you to lose by offering a bonus/incentive.
IF he isn't stick to your guns with the £18k only.
Keep us informed