All income is to be reported unless there is a specific code section that provides that it is not taxable.
You need to report this regardless of whether you received a form 1099. So you just report it as if you had received the form 1099.
You will report this on schedule C along with any other income and expenses you may have attributable to this business.
Be sure to keep good records, or even give your customers a receipt after you get the money.
The IRS is cracking down on taxpayers who claim cash income in order to qualify for EIC.