Firstly I do not do CPA, I am not interested in it in the slightest. What I do, do is affiliate for the most reputable bookmakers and casinos in the UK. Firstly I only stick to the most reputable bookies and casinos due to the fact I know they are not going to have me off over the sake of a couple of grand.
Here is most likely where you are going wrong. So you get 100 impressions a day, well where are those impressions coming from? Do you have a clue about keyword research? Here is what I target in the gambling niche "PLAY" because "play" is a buying keyword. a converting keyword. For instance "play roulette" "play roulette online" "play bingo" "play bingo online" "play what the fuck you want online" it does not matter how far down you delve into the gambling nice, if you go for keywords associated with play, you are targeting people who actually want to "play", they want to spend money gambling.
Now take your own niche, and ask yourself if you are targeting buyers, or simply searchers. Fish where the fish are, the big fish, don't fish in an empty pond. Simple.