[Pseudoscience-is-malarkey (OP)]

In guitar/music shops I always see acoustic guitars that pretty much look the same, (same size, the strings look the same, etc,) and will see easily see the contrast in prices. What makes some of them cheap, while others are expensive?

[Colin2B]

Depends
Materials vary a lot eg plywood vs solid wood, or a cheaper wood. With a solid wood front (which makes the biggest difference to the sound) an expensive guitar will most likely have a carefully selected set of characteristics.
Money spent on acoustic design and testing will produce a better sound.
Labour cost is a big one so minimum time on construction and finishing will produce a cheaper instrument, but less care on making sure all joints are sound and don’t introduce unwanted vibration or damping.
Time spent on setup and adjustment will make a difference to the sound, something not done on cheaper instruments.
Brand name. People will pay more for a name even though quality might be the same. Some manufacturers exploit this by running more than one brand.

Biggest and most important question is how does it sound. I’ve played some really cheap guitars that sound great, but the next one along - same make & spec - sounded terrible.
Play as many as possible and find one you like.

[evan_au]

If you have a well-known name, people will pay more for it, regardless of whether it is any better than the others.

This has led to some embarrassing results for self-proclaimed "experts", where, in double-blind experiments, they have been unable to tell the difference between:
- An expensive wine, and a much cheaper wine (eg one not produced in that valley...)
- An expensive musical instrument, and a much cheaper alternative (one case I saw compared a genuine Stradivarius violin to modern professional violins!)
- Vinyl records to CDs & MP3
- Coke and Pepsi

Of course, cheaper materials and production techniques may be used in cheaper versions, and they may not last as long...

Oops - overlap with Colin2B

[alancalverd]

65 years on, my boring Hofner Congress sounds as good and plays as well as it did when I bought it for an awful lot of money because the wood was well seasoned and the construction well engineered. My much flashier Spanish fingerstyle, with mother of pearl  inlays and all sorts of prettiness to appeal to tourists, fell apart when it was left in the sun because the glue melted - but it looks great hanging on the wall.

I sometimes get  to leave my £500 Chinese factory double bass at home and play a £10,000 Italian concert bass that fills the room with gorgeous sounds and no amplification.  You can buy a lot of amp for £10k, but not much hand-carved solid wood!

[Colin2B]

65 years on, my boring Hofner Congress sounds as good and plays as well as it did when I bought it for an awful lot of money because the wood was well seasoned and the construction well engineered.

Beautiful instrument, always sounded good and very consistent quality products.