When you go to test sew machines, take several pairs (about 8 inch square will do) of your own fabric to test with, that are the type you plan to sew. A lot of dealers show sewing on a stiff piece of buchram-type material that does nothing to show what you really want to sew.
Take several pairs into each shop. On the squares, sew a few rows of stitches, straight and decorative stitches you think you will use. Then sew a pair together using the machine's 1/4 inch seam foot or mark on the baseplate.
As soon as you are back in your car, mark on your test patches with a permanent marker, the brand/model of machine, and any other info you liked or disliked about the machine, and the price.
When you get home, press and measure your piece to check the (accurate) 1/4 inch seam.