I don't think there's an absolute, but most trainers I've spoke with who take deals, do so to get horses in the barn and because it's easier to do so when owners don't want to pay the bill(s). I am sure most of them think they will make out better, but then again, generally, horse trainers aren't great businessmen-----especially the majority that take deals, LOL. I think it's foolish for the trainer to take a horse on a deal unless the purses are high enough to make it worthwhile. At the lower end of any track, it just won't work for the trainer. I've seen many go broke.