Hackers aren't uncommon, unfortunately.
Also, you have to take into consideration that some people 'live' this kind of thing and spend an unbelievable amount of time online.
If BF3 is similar to Bad Company 2 then shooting through walls is possible (as it is on CoD games) as for seeing where you are, if one of there players flags you or your in the area of one of there proximity mines you will show up as a nice red dot on there map.
If you find your registering hits on people and they don't go down maybe your ping is a little high. Always look for servers with a low ping (30 ish usually)
When i used to work the night shift i would come home and have a few hours online and it was usually Americans at that time. Server pings would be 100-150 which was interesting. I would have to aim for where i 'guessed' the players were moving to. :lol: