If they will let you, take a few pieces of fabric, a drop cord, and some thread and sit and sew at a few. Explain to them that you want to try out the machines before purchasing and that you'll leave your practice piece at each machine so that others will see what that machine can do and they'll be able to sell them easier. They'll probably let you do it. Then pick out the best one and take it home.
You might even be able to work out a deal where if you do that on all the machines they'll pay you back by letting you take your pick at no charge. Tell them that if people could actually SEE what the machines are capable of that more would sell. Make sure you take contrasting thread and fabric. White fabric with red, blue, purple thread.