Checking it for what? If your extending them credit then they need to fill out a credit app. and you can submit that to the big 3 and get a credit score. I don't believe you can run a credit check for a monthly mow or fert etc. unless they agree to filling out an application. Easier way is to get a CC # on file with a contract that says if there x amount of days late with payment you can charge the card.
There are quite a few companies around that will run a bureau for you (for a fee of course). Google "third party credit checks". Typically you will need verbal authorization from your customer to run a credit check, but I would highly recommend having a 'mini - app' with a spot for their siganture and authorization.
A credit check is a good idea especially for larger private accounts or if you are going to be fronting material costs.