Can a buyer's own lender impose closing conditions that aren't even in the purchase agreement?

Yes, and this is a genuinely common source of friction in deals involving buyer financing. A lender financing the purchase has its own separate relationship with the buyer, governed by its own loan agreement and conditions, which exist independently of whatever the buyer and seller negotiated in the purchase agreement — a lender can require its own due diligence, its own security, appraisals, environmental reports, or other conditions that were never discussed with, or agreed to by, the seller at all.

This is exactly why a buyer's financing condition in the purchase agreement matters so much, and why a seller should think carefully about how broadly it's worded — a financing condition tied loosely to "the buyer obtaining financing on terms acceptable to the buyer" effectively imports whatever the lender demands into the deal's own timeline and risk, even though the seller had no say in the lender's requirements. Sellers can push for a defined financing period and evidence of a genuine, active loan process, precisely to avoid an open-ended exposure to a lender's own, separate conditions.

If you're a seller dealing with a financed buyer, get a Treadstone business lawyer to look closely at how the financing condition is worded before you agree to it.