Most of what I would call "consumer" grade carpet cleaners - ones you can buy at costco or sams club- tend to leave behind a soil attracting residue, don't rinse well, and tend to foam like crazy with higher pressure professional equipment.
You also do not want the customer to see you using something they see on the shelf at Wal-Mart.
You should stick with cleaning solutions from actual carpet cleaning chemical manufacturers like Judson - who participates on this board, Pro's Choice,
ProChem, or the
Matrix line from
JonDon (for example) until you get some more time under your belt for dabbling.
These complete lines of products will have chems that work as a system together - a prespray, acid rinse, emulsifier, protector, urine treatment, boosters, spotters, etc. You can mix and match from different brands, but buying from one source will help keep things simple when starting out.