There are a number of things.
Sometimes Roadsters will come in with a stamped service books. They usually get lost by the UK importer, who will attach no importance to them. If its present, a typical page will look like this: 
The exact format might vary; I’ve seen Roadsters with stapled in pages.
You can glean some information from this without knowing Japanese. Its a good idea though to get to know the Japanese year system (the year is expressed as the number of years the present Emperor has been on the throne).
That might indicate if a car has been regularly serviced; as you can see all it is is a simple check list, so its difficult to see if any extra work had been carried out. In addition, often when cars are freshly imported, they will have a vast collection of stickers on the door jam or under the bonnet indicating oil changes and brand. Often, importers remove these to tidy things up.
How to check if a car has been clocked before it entered the UK? Many Japanese auctions are now recordedd by BIMTA, who for a fee, will check what was the declared mileage when the car was auctioned. I’ve noticed on some auction dockets, if the auction house isn’t sure of the mileage (ie. there is no proof), they will insert “N/A” or “?” against the odometer line. I don’t know if all auction houses do this, or if it carries any legal responsibilities or consequences.
The same auction docket will also give a grading of the car, describing any damage and any panel repairs. From the pattern of repairs, you can make a decision if the damage was minor (eg parking scrapes) or something more significant; dockets showing boths wings, bonnet and bumper being replaced might indicate more significant damage.
eg. 
Panel damage codes:
A1 A scrape which is the size of a fist.
A2 A scrape which is the size of two palms.
A3 A scrape which is more than size A2.
E1 A dent which is barely visible.
E2 A few dents which are barely visible…
E3 Some dents which are barely visible.
U1 A dent which is the size of a thumb.
U2 A dent which is the size of a palm.
U3 A dent which is more than size U2.
Y1 A tear which is the size of a thumb.
Y2 A tear which is the size of a palm.
Y3 A tear which is more than size Y2.
W1 A panel which has been repaired slightly, and is in good condition.
W2 A panel which has been repaired slightly, and has a slightly wave.
W3 A panel which has been repaired slightly, and has a conspicuous wave.
S1 Rust which is the size of a fist.
S2 Rust which is more than size S1.
C1 Major rust corrosion which is the size of a fist.
C2 Major rust corrosion which is more than size C1.
X A panel which needs to be replaced.
XX A panel which has been replaced.
Exterior grading:
S Superior to Grade 6 or higher
6 or higher As good as new. Exterior and interior are in immaculate condition. Some cars in these grades have never been driven.
5 A car does’t need repair. A car has been repaired slightly, and the repair is in very good condition. No body parts have been changed.
4.5 A car has been repaired slightly, and the repair is in good condition. It becomes a grade-5 car with slight repair. There are a few slight scratches or dents.
4 A car is in good overall condition, but there are a few scratches or dents.
3.5 A car has some conspicuous scratches or dents. Some car’s head-light support panel or back panel have been repaired.
3 A car has many conspicuous scratches or dents. A car has some paint blemishes.
2 A car is in very bad condition
1 A car which has following
1. An aftermarket turbo
2. An automatic transmission converted to manual transmission
3. Flood damage
RA A car which has had accident damage which can be ranked MINOR, and has been repaired.
R
A car which has had accident damage, and been repaired. The auction definition “A car which has had accident damage” is a car where some parts or panels have been repaired or replaced or need to be repaired or replaced (or has some visible marks from frame damage) :
A
*** A car which has had accident damage, and has NOT been repaired yet. Or a car withan engine that does not work with major engine trouble.
Its changed somewhat from before, where cars were graded 1-5, with 5 being showroom condition. In general, a 4 might be a one owner car, with average wear and tear. Many Roadsters would be grade 3.5 to 4.0.
Interiors would be graded as well, A through D, with A being immaculate.
If the car has been in the country a while, chances are all this paperwork has been lost, so you would have to inspect the car more closely.