Can I get out of a signed purchase agreement if I find a deal-breaker before closing?

It depends on whether the problem you've found ties to something the agreement actually gives you a right to act on. Two main paths exist before closing: an unsatisfied closing condition (financing, a licence transfer, a clean due diligence result, or similar) that you're entitled to rely on, or a material-adverse-change clause allowing termination where the business's condition has significantly worsened since signing. If your deal-breaker fits within one of those negotiated rights, you generally can terminate without being the one in breach.

If it doesn't — you simply changed your mind, or the issue was already known and accepted when you signed — walking away is itself a breach of a binding contract, exposing you to the seller's own claims, including potential loss of a deposit. This is a genuinely different question from a post-closing indemnity claim, which only becomes available once the deal has actually closed; before closing, your options run through conditions and MAC rights instead. Get the specific clause language reviewed before deciding.