The latest generation K-bikes and R-bikes can have their firmware upgraded by the dealer but there's a finite number of times that can be done. THe early versions weren't so great and the bike's throttle response was poor.
Ask what version of firmware is in the ECU.
Ask how many times the firmware has been upgraded.
Ask the dealer what the latest firmware version is.
BMWs have a 3 year/36K miles warranty so if the owner doesn't know you should be able to call the dealer with the VIN and get the bike's service history.
You might also do some reading at
http://www.k-bikes.com/forums/cmps_index.phpand
http://www.i-bmw.com/