Instructor pilot reported a gear collapse on a familiarization flight where the flying pilot incorrectly raised the gear on the landing rollout. The pilots safely evacuated the aircraft after the aircraft came to a stop on the Runway.

Narrative

I discussed the trip with ZZZ FSDO to confirm my application of CFII privileges were appropriate without a medical. I was told yes; as long as the new owner is PIC. all this was communicated to the new owner prior to trip departure. New owner landed. Retracted gear on rollout. I was looking down the runway at rain puddles. I assume he thought he was retracting flaps since he came from a C-150 with a flap switch. We had just completed a cross country trip; ZZZ1-ZZZ over three days; which I accompanied him to provide aircraft familiarization. All went well on the trip. We discussed aircraft differences prior. He communicated to me he was private/instrument rated and had secured a complex aircraft endorsement from his CFI the Day 1 prior to departure; and that the aircraft was insured. Each landing was briefed for safety consideration; including gear operation. The new owner was short on experience; but confident. I otherwise watched him closely. He lacked disciplined SOP's. Short of saturation; he otherwise generally made a conscious effort to improve his procedures. I think contributing factors were complacency from landing a home base; and rain water contaminating the Runway. He knew of his mistake nearly immediately after placing the gear control in the up position. Corrective action was his attempt to prevent gear collapse by placing the switch back in the gear down position.