It is not that rare. I track down and kill some buffs, only to get some nice PMs like this:

(To tell the truth, they are often much less friendly than this one

)
How can someone flying in Lancs at 21k think he's invisible, only because he stays out of the dar circle?
Here now the explanation for those who think you have to use spies or shade accounts to find your enemy:

I sit in the tower, looking at the map to find out where to go next. I see a small darbar in the south
(1)Now I don't know if the con is heading towards N or S, or if he's going to A32. But at the 14,X line is a favourite route for bombers going to HQ or strats, I decide to wait a few minutes.
(2) The darbar went north into 14-12. It took relatively long for the darbar to move from one sector to the other, so it's a very high probability it's buffs. (All heavy buffs take about 6 minutes to cross a sector in a straight line). A single fighter would be very unlikely on that area anyway. So I'm quite sure it's a single set of high altitude bombers otw HQ or strats. I take off in a 163.
(3) I chose an ESE interception course, partly due to the Komet's high speed, but also because I still can't completely rule out the possibility that the unknown con is actually heading for base A31 itself.
A Me 163 takes about 2.5 minutes to get to 15k, I level out and stay just under the cloud level. After less than 3 minutes, I reach point
3. If my assumptions about the nature of the con are correct, it should be around here (as mentioned before, at 6mins per sector buffs flying in a straight line would be halfway through the sector. And bingo! I spot a high dot NE my position. Full power!
(4) Less than one minute later, the 21k Lancs are getting their unhealthy dose of taters.
No luck, no BS, no magic. Just watching the map and a very little bit of thinking. The enemy can't be "anywhere" in the sector. It's quite possible to give a very good estimation of his location just by the clues the map is giving you.