My experience is with our annual Bible camp quilt auction. You can't guess the color schemes in peoples' homes, but people always seem willing to spend money on quilts they can give as gifts to grandchildren. Therefore, smaller kid themed quilts with novelty fabrics are always popular. People like quilts with a wow factor. Also, quilts made from local team colors sell well, as do denim quilts, zebra prints, wildlife prints (for cabins), pink, purple, lime green, etc.
Disappointed donors are those who have put in a lot of time (such as hand quilting). The general public seems to be looking for eye appeal. Not too many are willing to spend enough to cover hand quilting costs, and the cost of a long arm quilter also may not be recovered with enough spare to make much of a profit.
These are just my opinions based on several years. However, localities and audiences differ. And if you are selling quilts to an audience of quilters, such as at a quilt show, that is completely different.