I had an ex-plod R80RT. When I was despatching I knew a few guys with ex-plod airheads and K's. These used to come straight from auction via a dealer (usually a man with a shed). The seat and panniers were the main and obvious things, however mine (and everyother one I saw) had modified electrics - ie all the plod lights, radios etc, had been fairly brutally removed - so loose wires, bare cables everywhere - and fairly crude butchering of the fairing where the auxillary stuff had been. The paint on the fairing was damaged where they had removed the dayglo stuff.
Mine had also been fitted with a callibrated auxillary speedometer, so althought it had done 50k, the BMW odometer was reading 00007. They should have a statement of mileage authenticity as of when they went to auction.
I bought mine from a guy who did nothing but deal in these. He reckoned that the state they came to auction in varied massively between forces, the day I bought mine he had several with 40-49k on the clock, all with leaking gearboxes, final drives etc. The forces that used to retire them at 50k would dump anything with 40k+ on if it developed any problems.