Forum:Eagle-Eye Mission

Any tips on how to complete the Eagle-Eye-missions in Arizona? I've made it to mission 27 but it is really hard sometimes: When the two dealers meet, one of them goes back behind the wall after just a couple of seconds and the sniper rifle can't fire the shots fast enough. I use the revolver sniper rifle, don't want to buy the eagle eye (too expensive and I'm not sure that would be better)