It's always a good idea to do an HPI check on the car, If he bought it from a legitimate importer he should have the BIMPTA milleage certificate which shows the mileage the car was at when it went through the auction house in Japan.Although it will be in KM but is easy to work out as miles. Also ask if he has the Auction Papers for the car too as this shows the grade of car 1 being poor and 5 being superb, has the car beem converted to MPH and de-restricted as Jap cars are limited to 112 mph by law.
Look out for the usual stuff, all panel gaps being even, no signs of filler or overspray indicating accident damage.
No smoke on start up or when revving, no nasty rattles from the engine, no nasty knocks when under heavy acceleration or braking. When braking hard make sure it pulls up in a straight line.
If you're not sure what you're looking for get an AA or Rac inspection done, these normally include an HPI report too.
The main thing is take your time look at lots of cars and don't dive in and buy the first one you see.