Re: "Maybe my dad was just rich and could easily absorb the cost"
I did start taking dog number six (Brutus) to the vet regularly and had checkups and bought flea/tick/mosquito prevention once he was around 7. Before then my attempts at curing a flea infestation involved rubbing diatomaceous earth on his belly: flea medication would have knocked it out cheaply and easily. Deurgh.
I have no idea how he beat the fleas. They just started to disappear one day.