I use a flag tip long handle wheel well brush and a carpet brush with a Tornador and OPC 20:1 to clean vinyl floors. The brush helps loosen the gunk out of the texture and scratches of the floor and the Tornador helps blast it into my waiting mf. I don't use an extractor or steamer for this except if something is really stuck on I will steam it or if it is really muddy I might wet it down first and suck it out. I like OPC because it is versatile and economical, and I also like the way the surfaces look after it dries off.
For a fleet level detail, to get the dark look back without adding too much slipperiness or getting too involved I use the Tornador with CG Silk Shine mixed about 3:1 with water + a splash of CG New car smell. The floors will fade again after awhile but it will look nice and new for your customer. I dress the entire interior this way as it is easy to control and you can do vents and buttons without having to worry about putting too much on and with the tornador it already uses way less product than you would by hand. If the interior isn't too horribly dirty I don't even use the OPC and I'll go straight to silk shine and the Tornador. Once the whole interior is dressed and dry, I do the glass and then go back over everything I dressed with a dry mf towel. Some folks would say not to use a dressing on the floor but the watered down silk shine works great.
If you have a stain, work it 2 or 3 times and throw in the towel before you ruin something.
Vinyl fleet rigs are easy to turn over and I love interiors. They're usually taken care of by the local scratch o matic car wash if anything and the interiors are usually not given much more than a vacuum and occasional windex. The vents, buttons, seams, seat tracks, and dash are usually caked with dust and the Tornador busts all of that out usually without even having to use a brush.. Big time saver. It also works on headliners if you're careful.
I am just a dabbler in (the expensive, addicting art of) detailing and have a day job so someone else might chime in with more experience than I. One word of advice, don't sell yourself short. We tend to see minivans on here as some of the big interior challenges but you may end up wading through just as many wrappers and spilled drinks in an econoline work van so make sure to see the rig before you give a price.