The claiming game is all about trainer tendencies.
DRF gives you some generic numbers: % off 1st claim, overall claiming win %. This is a start and can be helpful when dabbling. But, sticking to 1 or 2 tracks will allow you to really get a feel as to each trainer's intentions.
For example, a trainer claims a horse for say, 30K and is now running him for 20K. Is he dumping damaged goods or trying to steal a purse? If you can't make an educated guess you should probably pass the race.
You'll guess wrong many, many times because a trainer has to stay somewhat unpredictable. Like in poker, you can't raise only when you have the cards, you need to bluff now and again to stay honest. In the same respect, a trainer can't steal the purse every time...his horses would get claimed too often.
Hope this example helps.