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You should be issuing a 1099 to this individual. You can provide hime with a W-9 (see link below) to request his taxpayer identification number and other information which will be required on the Form 1099.
If the person refuses to provide the W-9 and taxpayer identification number then you are required to start "backup withholding" immediately. (i.e. a portion of the proceeds you pay him will go to the feds instead) Check out the article here from the IRS website.
Hopefully this provides the clarity you were looking for. Let me know if you have any further questions.
You should try and document that you have requested a W-9 from the vendor. This could be done via a fax confirmation or registered mail receipt. Once that is done, and you have no future business with him to perform back up withholding on, it is between him and the IRS.
Basically what the IRS is doing is trying to ensure that everyone reports their income. If you pay him more than $600 in a year you should issue him a 1099. This 1099 also gets reported to the IRS. They will then ensure that he declares the $600 on his tax return.
If you are audited the IRS can disallow your expenses paid to him if you did not issue the 1099.
Hopefully this helps, let me know if you have any further questions.