This takes me back. I suspect many of us have done two games in a day when we were starting out as referees. I sometimes did a schools game on a Saturday morning then a local league game in the afternoon. Then another game on a Sunday morning.
It was not a regular thing for me but I knew one chap who did two games every Saturday then two every Sunday, simply because he needed the money. He only had one set of kit! Also, he didn't drive so relied on buses or scrounging lifts between grounds.
As I have mentioned before, I also refereed basketball and there were people who would referee almost every day, sometimes doing two games, one after the other, at a venue. It paid quite well and some people must have been coining it!