Aramsco Interlink can rent the equipment and provide training to a cleaner who scores the occasional garage or convinience store polishing job, but they have to purchase the diamond abrasives, so there is an investment.
The first 3 steps to grind down and totally expose the aggregate are metal bond diamonds that cost about $120 each and you need six for the smallest rental grinder. The epoxy resin polishing grits are about $35 each and those steps are 4-8. If the concrete is dull but not deeply scratched you don't have to start at the lower, more expensive grits.
I know two carpet cleaners personally who totally divested from their truckmounts after doing a few jobs. This was even before I started working as an Aramsco sales rep.
Concrete polishing is not for everyone though. You need a strong personality and when setbacks happen there is no pouting. Carpet cleaning is hard too, but if the homeowner doesn't like the job you did, you can usually walk away and they'll call someone else. Jack up a concrete job and word spreads pretty fast...
I do free training out of Las Vegas. Anyone is welcome to come by for an afternoon if they are interested.
Rob