
The fabric decides the shape, the comfort, the life of the piece and a large part of the cost. And a fabric mistake cannot be fixed by sewing.
Ask for fabric swatches before any decision. Wash a swatch once or twice as your customer will, measure the shrinkage and watch the color. Crumple it in your hand to see how it recovers.
For every fabric in your collection, write its composition, weight, likely supplier and your note after the wash test.