Small houses are not necessarily hard to sell, though it depends on a few factors:
The #1 home selling mistake we see is when a home is not priced appropriately. Listing too high will result in many would-be-buyers not even inquiring. Many will wait for possible price drops or keep looking at other options. What's more, many buyers have firm maximum price limits and won't even consider or be altered to your listing.
To sell your house fast, you need to price it at an attractive point to draw in as many buyers as possible. This means carefully analyzing comps.
In your local there are likely many people looking for houses for sale with 1 to 2 bedrooms and 1 bathroom. But if we're talking about a tiny house (100 to 400 square feet), then the market of prospective home buyers is probably also tiny.
If your house is designed in a manner that very few people find appealing, then you would need to reduce your asking price in order to sell in a timely manner.