Does signing an LOI stop me from negotiating better terms later?

Not on the terms themselves, generally. Because price and structure are typically non-binding in a business-sale LOI, signing one doesn't usually prevent you from proposing changes later — pushing for a better price after due diligence turns up new information, or renegotiating structure as circumstances change, is a normal part of how these deals evolve between an LOI and a definitive agreement.

The practical complication isn't legal, though — it's leverage. If you've also agreed to an exclusivity clause, you've given up the ability to negotiate with anyone else while you try to improve your position with this buyer, which weakens your bargaining power compared to before you signed. A buyer facing a seller who keeps pushing for better terms may also become less cooperative, slow down the process, or reconsider their own position, even though nothing legally stops either side from proposing changes.

The nuance worth planning for is that renegotiation works best when it's grounded in something real — new information from due diligence, a changed circumstance — rather than simply pushing because you can. A Treadstone business lawyer can help you understand where you actually stand before you try to reopen terms.