Similar-ish thing happened to us - the wooden flooring had warped but my husbands desk was on it so we didn't know until we moved out. We told the agent as soon as we saw it and negotiatied with the buyer. We waived their occupational rent for 1 month to compensate.
Ja, most people act in good faith. BUT the voetstoots clause will protect you, the onus is on the buyer to move the desk and check everything. You are only liable if you hide something deliberately.