If a sole proprietor has employees, IRS requires a separate EIN, but the sole proprietor still has all tax liability as an individual. I think he can have an EIN without employees if he chooses to do it that way in order to have a checking account in the name of the business. If he's using credit cards for virtually everything, he may be using his rewards points for cash rebates and using the credit card statements to help in his recordkeeping. I had a situation a year or so ago with a customer depositing wrapped gold dollars in $2-3k increments every few days. Turns out, after the detective did some investigating and finally sat her down (SARs filed from every bank in town per the mouthy detective) that she was using an AmEx Black Diamond card (I think Black Diamond? Definitely AmEx) to purchase the coin at face value from the US Mint with no shipping/handling costs and racking up enough rewards points to pull in about $30,000 a year from AmEx. It some 'get rich thing' she found on some website, it was perfectly legal, the US Mint wasn't happy about all the people that were doing it, but she was doing it purely for the cash rebate from AmEx for using their card. Your guy may have figured out that using his credit cards is good for cash rewards.
On your landscaper, I'd find out if he's got any employees or if he's a one man operation. Since you're not seeing any evidence of employees and it doesn't sound like he's pulling enough cash to make a cash payroll, I don't think you've got enough info to file on him. Yet. I think you've got questions to answer first.
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CRCM|CAMS