If they're in the US, a lot of financially smart and motivated people can play Credit Card games to maximize on their miles / rewards for purchases such as like 3% cash back on some purchases.
I have a friend who's honeymoon was completely paid - first class flights and ~three weeks worth of all inclusive 5 star hotels/resorts - all on points.
His father ran his entire construction company paying everything he could on the highest rewards based credit card available at the time. He apparently put over 12 million through it in two years. (I suspect it was about an order of magnitude lower than 3% cashback on that, but it was still a nice chunk of honeymoon and travel bills paid "for free", or more accurately by the bank and their merchants, and probably at least somewhat passed on to the construction company's customers in prices high enough to cover the credit card rewards scheme...)
His father ran his entire construction company paying everything he could on the highest rewards based credit card available at the time. He apparently put over 12 million through it in two years. (I suspect it was about an order of magnitude lower than 3% cashback on that, but it was still a nice chunk of honeymoon and travel bills paid "for free", or more accurately by the bank and their merchants, and probably at least somewhat passed on to the construction company's customers in prices high enough to cover the credit card rewards scheme...)