You don't need one, but you should have a literary agent or an attorney to help you negotiate any deal.
Wow that was easy!
But seriously, it's clear that I'm biased—this is my job after all! We agents earn a living by negotiating deals for our clients, including deals with smaller presses. I talked about some of the contract stuff that agents take care of in an earlier blog post, but we're going to get more into the weeds on this post.
One of the most important facets of literary agenting is negotiating the contract you have with your publisher to make sure that you aren't being taken advantage of. We (agents) deal with contracts all of the time, and because of that, it gives us some institutional knowledge of what goes into a publishing contract, what terms are acceptable, and which others make no sense at all. I'm sure there are lots of resources online to help authors with some of these things, too, but there's a secondary reason why agents, not authors, negotiate.
Agents get to be the bad guy. Let's say you, as the author, are negotiating your publishing agreement and you're adamant that you are not going to grant merchandise rights (which should be the case in most deals). Now the the publisher pushes back, and you're faced with a dilemma: in order to protect yourself, you have to be stern to your editor, thereby potentially harming the relationship between you and your editor. Agents don't have this issue. Our only job is to protect you, the author and our client, and get the best deal possible. When the negotiation is over, despite how awful it was or how many phone calls we had to have, none of that reflects on you as the author. So you and the editor can still go to lunch (barring a pandemic) and laugh and both complain about the contract process. I'll take the blame as your agent!
"But wait! I love my smaller press and we have a great working relationship. I don't have any issues with my contract!"
That's great, and I'm happy that you've found a reputable company to work with. But contracts should, by their very nature, contain a lot of "just in case" language. Contracts need to protect you and the publisher in as many eventualities as possible. Otherwise, there's no basis for what to do if the fit hits the shan. And if the worst does happen, can you trust the company that cares about making money to protect you over themselves? I'm not saying it's impossible, but it's unlikely.
I like to call it "just in case" language because 99.9% of the time, it's never going to come into play. Do I expect the publisher to cancel your contract? No, of course not. However, I'm going to make sure the language allowing them to do so is only applicable in very certain circumstances.
It's our job to push and ask that arbitration language be amenable or that you're covered if the publisher goes bankrupt or that the force majure clause is complete or that the option isn't onerous. And this is just some of the legal language that goes into a publishing contract.
I'm negotiating deals with two "smaller" publishing houses right now. The draft contracts that were sent to me were 8 and 15 pages, and my notes for each of them were an additional 7 and 8 pages. I hope that most of the additional language or changes I've asked for never has to be used at all. But I still want it in there to protect my clients.
Can you negotiate your own deal with any publishing house? Of course you can. But you should, if you can, get some help with it.