Many professionals can provide a valuation service.  In aviation, it is often the case that pilots will take on the added responsibility of providing a valuation service to their clients.  Their opinion normally comes from anecdotal data collected during discussions with other pilots and / or perusing the various magazines that are used to buy and sell aircraft, an example of such being Trade-a-plane.   While this may well be enough for the client it does not take into account the steps and processes that a professional appraiser following USPAP (The Uniform Standards for Professional Appraiser Practice) will need to perform.

If you need a more analytical and thorough approach to you opinion of value it will serve you well to hire an appraiser.  The professionals at Zeus have decades of experience with all types of aircraft and engines.  In addition their long standing exclusive partnership with Starman Auctions provides a conduit to the liquidation side of the market.