General mountain dulcimer or music discussions
I would absolutely tell anyone with no dulcimer experience or first hand technical advisor NOT to buy a dulcimer kit from anyone.
If you don't really know what you are doing, shop in a face-to-face setting where you can try out the instrument and discuss it with the seller. Preferably the seller should demonstrate the instrument.
I suspect that the "unplayable" Applecreek dulcimers primarily need a proper setup. It is common in the music world for factory made instruments to be shipped with the expectation that the selling dealer will do a setup to meet the customer's needs. This is primarily adjusting string height, but also may involve other details. In the ukulele world, string heights are typically too high because lowering them is easy, but raising them isn't. This is probably true for most low priced fretted instruments. If you buy such an instrument, the retail dealer, not the manufacturer or wholesale distributor, is responsible for assuring that the instrument is ready for use.
Wooden instruments can, or will, change between the time they are built and the time the first owner begins to play them. Woods bend, and exposure to string tension can also alter them. No builder can predict the changes.
Generally speaking, if you are ordering an instrument costing $500 or so directly from a well established builder, it will probably be checked and setup before shipping. This is partly because the builder's reputation is at stake and partly because the builder is doing retail business.
For those with a good musical ear, I suspect that if the heights are just a bit high a dulcimer set up with (common) 0.012 strings and which plays "OK" in DAA tuning might be irritating if tuned to DAD, but OK in DAD if restrung with 0.010 melody strings. Correcting that sort of thing is "setup." My opinion on that is based on 70+ years of playing string instruments, training in physics, and amateur building of a variety of fretted instruments. It's not "Rocket Science," but it is precision technology.
I have seen dulcimers from semi-pro builders which were NOT properly set up. Knowing wood working isn't the same are knowing lutherie.
With regard to natural wood versus cardboard versus laminated construction, you should not generalize. All need setup, whether by the builder, retailer, or buyer.
Our local dulcimer group instructor bought a batch of cardboard dulcimers for loan to students. They have served us well for a decade or so, but this is because her guitar player husband spent hours doing the setup, as well as some assembly. She also purchased a group of Applecreek instruments, but again they got an adequate checkout.