Your agent needs to be a pig, not a chicken.
You know where this is going, right? When you sit down to a plate of bacon and eggs, consider the fact that the chicken is involved, but the pig is committed.
There are a few good and reputable agents around - as in they sell books to major houses, often for major money, and they make no upfront charges, i.e. meet the minimum standards any writer should demand - who are, nonetheless, chickens. They float the project a bit, and if it is not an immediate winner, as in it will make them a few bucks and not cost them any, they drop you. Excuses tend to run from the lame - I want to spend more time with my family - to the exotic, I’ve been elected president of the parakeet society and it is hugely demanding. Whichever, commitment this is not.
One of the ways you can tell if this will happen to you is to have your antennae alert for any suggestion that the agent will read the ms when he has time, but meanwhile he’ll run it by a few likely editors and see what kind of comments he gets back. No matter how desperate you are for representation, run don’t walk in the opposite direction. This agent is saying that he’s not sure the book has merit, but it might. Probably needs some work. But rather than pass outright on a possible profit opportunity, he’ll see if maybe his reservations are ill-founded and it will be an easy sale. Cluck, cluck, cluck. Meanwhile he’s burning your potential editors. As in the good agent who eventually takes you on won’t be able to go back to them with the ms once you’ve rewritten it.
To be absolutely clear, not every agent with every project suggests revisions. That’s not what this is about. You can separate the I-think-it’s-ready type from the tentative maybe-I-don’t-want-to-get-involved type by one marker, enthusiasm. So what’s the oink reaction?
Either the pigs are enthusiastic, full of plans for marketing, etc., or they say I like this, but I see some weaknesses. If you’re willing to revise, call me and we’ll talk about what I think the fixes to be. Or some variation on same. It means the agent is committing time to making the project as good as it can be. He/she knows there’s going to be some back and forthing, a few calls, revisions to be read and commented on…
Time is a large part of the agent’s capital (the rest is reputation/clout) and they are justly unwilling to squander it, but if they will spend none on you, keep looking.