Be sure to take your own quilting cotton with you to demo each machine.
The "cardboard like" "fabric" a lot of shops use to demo with is almost a sneaky trick: even horrible machines will sew a nice stitch on it.
Using permanent ink, write the brand and model number on each fabric as you play with each machine. Besides sewing two fabrics together/through, consider taking a pre-made sandwich (fabric-batting-fabric) with you as well.
I'd stay away from any dealer who doesn't want you to use your own fabrics.
Also be aware that if a machine isn't on sale, you can almost always make a deal for a lower price. Or just wait for a sale.
Good luck with your hunt! And have fun! If a machine isn't fun to sew on in the shop, it will be worse at home.
FYI ~ I have a Husqvarna 875 Quilt with all the bells & whistles including a thread cutter which is really useful: I love my machine.