When I had my Upholstery shop I used a Pfaff 545 with a walking foot. The walking foot is different than the one we use on a home sewing machine. It consists of two separate feet. I had it converted to use Singer feet because of the cost of the feet. Pfaff feet were like $50 and up for the different feet I needed for work. As it was Singer was sometimes 75% less in price.
I had to use several different sized welt (cording or piping) feet, a double welt foot was a must have. Then my walking foot set up, a regular flat foot for everyday sewing, and several more I don't recall what they were.
Having one in its own table and the heavy duty motor mounted underneath is ideal. Make sure the table is solid and level and no signs of warping.
I have seen several industrial machines on Craigslist so they are out there. Take several different types of fabrics with you, nothing to thin to the machine will just eat it up. If you have a piece of leather bring that and double it up or even triple layer it. It should go through the leather with little resistance, I loved that in my machine.
Most important is watch your finger placement. These machines runs faster than our home sewers. And it is VERY easy to run over a few digits before you know it.