The Sancheng 1:20.3 Brass Construction "Betsy" Locomotive is a high-quality, detailed model known for its craftsmanship and brass construction, often prized by collectors and enthusiasts of G-scale model trains. Here are some notable features of this particular model:

1. Scale and Gauge: As a 1:20.3 scale model, it is designed to represent narrow-gauge trains (typically 3-foot narrow-gauge) and is compatible with G-scale tracks, making it suitable for garden railways or indoor large-scale layouts.

2. Construction and Materials: Sancheng is known for its use of brass in its model construction, giving the locomotive a realistic weight, durability, and detail. The brass construction is often hand-assembled and sometimes even hand-painted, adding to its unique craftsmanship and authenticity.

3. Detailing: The "Betsy" model typically showcases intricate detailing that includes accurate rivet patterns, smokestacks, piping, and cab interiors. Such fine details make it visually striking and true to the prototype locomotives it represents.

4. Functionality: Sancheng models often come with working components, such as functional couplers, realistic wheels, and sometimes even DCC compatibility for advanced model railroading control. This makes it an operational as well as a display model.

5. Collector's Appeal: Sancheng's brass models, including the "Betsy" locomotive, are highly sought after due to their limited production runs, which adds to their value among collectors. They are also known for their realistic aesthetic, making them valuable both as display pieces and functional models.

6. Historical Representation: The "Betsy" model represents a smaller, industrial-type steam locomotive, often associated with logging or mining railroads of the 19th and early 20th centuries. These types of locomotives were known for their compact size and maneuverability, ideal for narrow-gauge tracks in rugged terrain.

Due to the hand-crafted nature and the high level of detail, these models can be fairly expensive, with value depending on condition, rarity, and specific detailing features of the model.

A brand new, never-assembled Sancheng 1:20.3 Betsy Locomotive in its original packaging is quite a rare find, especially considering that Sancheng (also known as Samhongsa) ceased production due to issues with U.S. distribution. Here’s what impacts its potential value:

1. Condition: Since it’s completely unassembled and untouched in its original packaging, this pristine condition alone greatly increases its collectible value.

2. Rarity and Demand: Sancheng models, particularly the 1:20.3 Betsy, are sought-after due to their quality craftsmanship, intricate detail, and brass construction. With Sancheng no longer producing trains, this model has likely become rarer over time.

3. Market Trends: Similar high-end, brass, narrow-gauge locomotives in unused condition tend to attract collectors, sometimes selling between $1,500 and $3,000 or more depending on the specific model and buyer interest. Given the limited availability and condition of your Betsy, it could fall into the higher end of that range or even exceed it, especially if a motivated collector is looking for a pristine model.