Hi welcome to the forums, not sure whether you are aware of this site:- http://www.bimta.co.uk/default.asp
Its a basically mileage check etc for imports, theyrs quite a lot of clocking goes on with imports and a few unfortunate incidents thru-out the jap forums, be sure to check it out. Im in a similar position to yourself, looking to buy an import, personally im going to use GT Culture i think as id like to see the car before i hand over all the money!
Other good importer Newera, bit expensive tho,also jurgen on these forums has a good reputation for quality cars, not sure on Bonsai cars tho, im sure somone else on here will have experience of them!
Good luck!