I sort of cheated the system. It blew my mind and I found it absolutely ridiculous how the game was based on nothing but luck. In the old games I didn't have to depend on luck, I could just buy the coins, but this game? No way.
I got up to about 1500 coins before I got bored just by playing level one, collecting my coins from all the rows and columns that didn't have a Voltorb in them, and starting over.
Sometimes I'd get 12, other times, I get 8, 4, or even 3, but it all adds up. I don't even know why I did this. The only pokemon worth getting that I can't immediately catch is Dratini, and it doesn't even have a place in my party. I guess it was just to prove a point.
Also, I found this, and I'm sure I'm not the first one, but it helps if you're just in it for the coins and not the game itself like I was.
It's not 100% every time, but it definitely got me up from 1200 coins to around 7,000 when I was still deciding between Mr. Mime or a Porygon.