The AFK report system in BG does not work well, and it often takes too long to boot players who deliberately AFK. I suggest implementing a system that automatically ban those who have been AFK kicked from BGs a certain number of times within a certain time period. For example, getting kicked from BGs through the AFK report system 3 times within a 24 hr period automatically results in a 1 day ban. The ban duration may increase for repeat offenders.
Or, perhaps implement a replay feature similar to that of Starcraft's. After completion of a match, you can submit a ticket with the match ID for GM to review the gameplay. If there are technical limitations, perhaps certain data can be omitted to minimize impact on server load while still preserving the "big picture" so meaningful determination can be made by a reviewer.