Not everything devalues as quickly as you may believe. Big gas motors, YS pattern motors, high quality servos (gears can be cheaply replaced and pots cleaned), good giant scale models, F3A models, retain value fairly well. Well kept, high-end radios too. Lots of models, especially big ones, actually go up in price from a total of their components because people are selling their work too (great if the work is professional in quality). I think in hobby terms that useful life remaining has more to do with cost than simply being used. Heck, a good gas motor might just be considered broken in after a couple of season's use, or a well treated Moki 1.8. 5 gallons through that motor is the break-in. No, hobby items are not like used cars. Perhaps like a used top of the line Mercedes. You can buy a used one for a like new price!!! Yep, meant that backwards.

However, I have not seen any outrageous deals like you are describing. Stay away if they sound bad. Don't pay more for used unless you are paying for quality labor. I would not expect to find too many $300.00 63" Split-Window Corvettes sold as a "used chevrolet" by the nice little old lady who's son was killed in the war shortly after he bought it (famous urban legend that a few thousand old farts are going to swear on their mother's graves that it happened to "their buddy"...I heard it everyday for the ten years that I drove an old Vette...that and the old story of "...so I taped a hundred dollars to the dash board and told him that if he could grab it before I hit 80 it was his"...LOL...gotta love these guys, like they were driving a Saturn 5 Stage 1 booster rocket). Please, tell me another!!!