I've tried using them multiple times. They have never worked. I have never been investigated.
This leads me to three generalizations about 'Booster Gifts":
1) Unless you actually sign the player, you probably won't get caught.
2) The chance of them working is between slim and none, and if you are lucky enough to be in the slim catagory, you will more than likely get nailed.
3) They are an absolutley useless tool that should be eliminated unless they increase the possibility of them being successful and reduce the possibility of being caught if they are.
I'm not saying they should always work but I'm saying they should at least work 10-15% of the time and the odd's of being caught should also be 10-15%.
This would at least make it worth the risk/reward.