ALBANY — Eliot Spitzer has returned a $50,000 contribution to a billionaire recently indicted on a prostitution charge and another $50,000 from a businessman fellow Democrat Hillary Rodham Clinton once called the “biggest polluter in America.”

Sending back such big checks is becoming more commonplace on the American political landscape, experts in campaign fundraising said.

On Wednesday, Republican-Conservative candidate for governor John Faso called on Mr. Spitzer, a Democrat, to return the $50,000 from financier Jeffrey Epstein, the New York billionaire who faces a prostitution charge in Florida. Mr. Spitzer campaign spokeswoman Christine Anderson said it was already returned and state elections records verify that.

Mr. Spitzer’s campaign this spring also returned $50,000 from Ira Rennert, a Manhattan-based millionaire businessman, Ms. Anderson said. Because of an oversight, she said that return hasn’t yet been recorded in state Board of Elections records, but she said it should be recorded in the next required filing, due before the September 12 primary.

“When you are fortunate enough to have such wide support and a very successful multimillion dollar fundraising effort, then it’s not unusual that a small amount will occasionally slip through the vetting process,” Ms. Anderson said. She notes Mr. Spitzer has also voluntarily returned hundreds of thousands of dollars more because of he won’t take contributions from those who are a subject of his investigations as attorney general.

“When a situation or mistake is brought to our attention, we respond immediately and the contribution is returned,” she said.

On Wednesday, Mr. Faso, who is well behind Mr. Spitzer in the polls and financing, said it is bad enough that Mr. Spitzer accepts campaign contributions from labor unions and others who Mr. Faso said “want to raise taxes. But it’s quite another to take money from somebody accused of soliciting prostitution.”