Programmer here, if they where truly honest. All they would have to do is to hash the binaries that run in their voting machines during the election. Then compile the same version of the code, after a full audit, in court. If and only if the hashes match exactly they can be considered innocent on the claims about internal manipulation.

But all in all, it's a shame to even allow proprietary code to run in a voting machine in the first place. Not even third world countries would sink that low. A company's profit and intellectual property should never stand above the election integrity.