Ask Daphne! I’ve been here before…

Shoes for a turn around the dance floor for Marina, who asks:

Should an unpublished author seeking an agent mention in the query that he or she has been agented before? Is there any benefit to doing this or not? I’d love to know your opinion.

Since an agent is like a partner (and I’m still working on my “writing is like dancing” presentation), I think these dance shoes are particularly apt. And much as having a partner for a couple of turns around the floor may indicate to other possible partners that you know what you’re doing, so do can mentioning you’ve been agented before. What you need to be very clear about, however, is what project we’re talking about.
Say you wrote Novel A, a YA urban fantasy, and landed Agent Q. She loved it, went out with it to all the major houses, but wasn’t able to get a bite. Crushed, you worried if it was Agent Q, not your manuscript, that was getting all the rejections, and so you cut your losses and moved on. In a scenario like this, if you’re now submitting Novel A to other agents, you absolutely need to tell them not only that it was previously represented, but that it was submitted widely. Unless there’s been a sea change in the industry, the manuscript, or a lot of time has passed since it was submitted, most agents won’t want to sign on a novel that’s already made the rounds.
But say Novel A got all those rejections, but while Agent Q was shopping it around, you were hard at work on Novel B, a middle grade detective novel. It’s quite different from Novel A, and for whatever reason, Agent Q decided it wasn’t for her, leaving you free to submit elsewhere and releasing you from your contract with her. I still think you should tell the new agents you’re querying that you were represented previously, but now we’re talking about a new and exciting project that hasn’t made the rounds. It’s not old and tired, and your new Agent X might be able to go back to some of those submissions that Agent Q made and resubmit.
I could keep coming up with scenarios, but the point is: yes, tell any agent you’re querying if you’ve been repped before. Not only does it tell them you know how to do the dance, but it also reveals that someone else thought you were a pretty good partner. And if another agent thinks that, so, hopefully, will an editor.