Can a private pilot, qualified to tow gliders, tow them when a charge is made for the tow?
Yes, a person who holds at least a private pilot certificate and who meets the requirements of Federal Aviation Regulation (FAR) Part 61, Section 61.69, may tow gliders whether there is a fee being charged by the towing operator or not. You can find additional information in FAR Part 61, Section 61.113(a) and (g).