How to get sushi coins faster?

I just started this game and as in almost every 2nd Kairosoft game you first have to find out how this and that works. Now I learned that the sushi coins (the special currency as in every kairosoft game) is again really important and you should take care of getting them really quickly and in particular get a lot of them!

So I noticed customers generate them at for example vending machines or by paying the bill. But I get the coins really randomly and it seems to me that they are very rare.

Is there a way to get the coins faster for example by making the customers more saitisfied with the food or is there a special time when every customer generates a coin or anything like that?