Paul,
Given that you are a newbie I should have given you a more thorough answer.
If you're going to be cleaning commercial upholstery then you have to be ready to do whatever it takes to get things clean. Prochem Pure Clean is a good place to start, but it might be necessary to spray the arm caps with fabric restorer and quite literally scrub it in. If it's restaurant seating you may need Powerburst to shift the grease which is often heavily engrained and that too might need to be scrubbed in to get a perfect result. You can also use brightening additives to bring out the colours a bit.
The problem is that if you're only using water in your machine then you cannot use the likes of Powerburst because it is a quite strong alkaline and needs to be acid rinse with PC's Fibre & Fabric Rinse or HM's Clearwater Rinse, both of which a liquids.
You have to experiment at bit with the first chair of each type and find a way to unlock the soil. And don't forget, quality is in the detail, If you don't get the piping, seams and difficult to get at pieces they will stand out like a sore thumb when the fabric dries.
Simon