The original owner of our firm seemed to have no rhyme or reason to his fees, until it hit the new owner and me that he was often charging based on ability to pay. That applied mainly to wealthier clients, who had exorbitant fees. Those with six-figure incomes with little more than W2s, Sch A, and bank interest were on the hook for $600 or more (and this was 20 years ago). A family-owned group of businesses that was making tons of money was charged triple just for monthly bank reconciliations compared to our other business clients. When he sold the firm, some of the clients did question their fees. We reduced most of them, many before they asked. So charging based on ability to pay works both ways.
Like most of us, I do a bit of pro bono work and have a few clients whose fees I haven't raised in forever because I know they are struggling. For the majority, though, I am not one to give away my work. I have professional credentials, years of education and experience, and I give every return the time including research if needed to best serve that client. For this, I should be paid. We don't have many EITC clients, but even though they are low income we don't undercharge. There are risks involved with that category, and the extra due diligence takes time.