Does 'to the seller's knowledge' protect a seller who just never bothered to check?

It depends on exactly how the knowledge qualifier is worded, and this is precisely the drafting fight that separates a strong knowledge qualifier from a weak one. A qualifier limited to what named individuals actually, subjectively knew — with no obligation to have made any inquiry — can genuinely protect a seller who simply never checked, since the seller is only promising what those people actually knew, not what a diligent inquiry would have revealed.

Buyers generally push back hard against that version, and instead negotiate for a "constructive knowledge" or "deemed knowledge" standard, which extends the qualifier to include what the named individuals should have known after making reasonable inquiry of relevant staff and records. Under that stronger version, a seller who deliberately avoided finding out about a problem, or simply never bothered to look, doesn't get the benefit of the qualifier the way it would under a purely actual-knowledge standard.

Which version you're actually signing up to matters enormously, and it's easy to miss the difference in dense boilerplate language. Have a Treadstone business lawyer confirm which standard your agreement actually uses before you rely on it.