We picked up an original 22 Center door about 7 years ago for around $6000. It was all original and had been in a barn from 1931 until we purchased it. It ran and drove. We have since rebuilt everything mechanically on it. We have almost into it as we purchased it for and I wouldn't sell it for less than $15,000 which I doubt anyone would pay for it, which is fine because it is so much fun to drive.
$6000 to $7000 is a steal for a rebuilt car; if the engine were rebuilt or was it just 'rebuilt'? Same goes for the rear axle. Ask him if it has aluminum pistons, new cam, new valves, balanced crank and pistons, new neoprene seals or the old felt style. Has the transmission been balanced, new starter ring gear, new field coil, new bushings reamed to what dimensions, drums checked cracks, magnets checked for cracks and recharged, what type of clutch is used, repoured fourth main, pan straightened on Wilson pan jig? New bronze thrust washers in rear axle, what is the ring and pinion mesh, balanced driveshaft, new u-joint or a near new original, new sleeves, axle bearings within tolerances or did he use the junk repop ones? My questions would go on and on; if he isn't sure buy it like you may have to rebuild all over again. Is the roof vinyl or the correct masonite type fiberboard? The seat cushions have been replaced, but I assume you realize that.
I don't want to burst your bubble, I just don't want you to get burned like so many have before.