Matt McGowan of Frances Goldin Literary Agency

Most of the material agents see is not professionally edited. However, it’s not unheard of, and the instinct to have your work looked at is a good one, as you really want to get it into the best possible shape you can before submitting it to any agents, magazines, or book editors. If you’re okay spending the money, I’d suggest you find an editor who can provide references, and I’d talk to clients he or she has worked with to judge if it’s worth it. There are plenty of former book editors who freelance now and who have the type of expertise you want.