advice with selling a car

[ebv8]

i have my old VH commodore forsale
problem is I have 2 guys wanting to look at it this thursday
1 if from QLD and is flying down to look and the other is coming up from goulburn (i'm in wollongong)
I have already taken it to a mechanic for the QLD guy (his brother inlaw) and the he said he was very impressed, so as long as he is happy he should buy it (why else would you come all this way) and the other guy has called me numerous times and his son is really excited about the car but can't get here till thursday.

do i just sell it to the first person who turns up? what if it sells and the other guy is on his way to look?

what is the right thing to do?