Apply the same principles to the interior of the aircraft as you do the exterior. Take time while the aircraft is powered up to functionally check every system in the aircraft (in today’s world that means manual seat adjustment, cabinetry latches and all door operations), check all lighting, switches, entertainment systems, monitors, galley equipment and water systems. All systems must function within maintenance manual allowable tolerances as dictated by the manufacturer or as they are operationally equipped. No items can be deferred in a pre purchase situation.
If there are systems installed, but placed in an inoperable condition due to operator requirements then you should give consideration to technically removing them and seeing that they are not advertised at the point of listing the aircraft. We see this with systems such as DVD and fax machines. In some cases they were originally installed never used much and when they broke due to lack of use they are never repaired. Operators feel, justifiably so, that they do not affect airworthiness and are costly to repair so nothing is done. In a pre purchase they can be written up as a discrepancy (not airworthy), but an installed system on the equipment list and will have to be operable. The same holds true of galley equipment. Any collared circuit breakers or inoperable lights or switches will have to work.
Be sure to check water drains and lav area for any signs of leaks or staining. Pay particular attention to lavatory areas above and below the floor. One of the biggest stop signs in a pre purchase is to find evidence of blue fluid in any area no matter how minimal. If possible, take time prior to inspections to remove all stains and address any leaks no matter how minor.
Cosmetic issues such as frayed carpets and worn leather or fabric will not need to be addressed, however, it is a good idea to have things cleaned and detailed prior to input. Facilities will write up some cosmetic issues and although they will not be required repairs they detract from the overall impression of the aircraft.
Prior to input it is also a good idea to determine what will be sent to the pre purchase with the aircraft and what is personal loose equipment that will be removed. A good rule of thumb to consider – anything listed in the weight and balance equipment list such as life rafts, life vests, head sets and portable breathing equipment should be left on board (with paper work) unless special arrangements have been made in the contract. Items such as Medaire kits, umbrellas, blankets, china and crystal can be removed. If an operator has a Medaire subscription and the kit it is removed there will most likely be a discrepancy written for lack of a first aid kit. A minimal one should be added prior to input. It is a good idea to check tags and certification along with placards for all hand held fire extinguishers. Along with that all original placards for evacuation, seat placement and door and cabinet operations should be checked and must agree with the original STC or certification of the interior regardless of 91 or 135 certifications. Any cabin equipment operational manuals should be made available to facility personnel so things can be accurately checked for operation. I see many discrepancies written for equipment operation that are in error due to the lack understanding on the part of the maintenance person. The prevailing thought here is to keep the discrepancy list to a minimum, anything written up right or wrong must be dealt with by the facility to be cleared in the eyes of the buyer.