Ask for the VAT number and check on the Revenue Agency website if it is active. You can also make a survey .. to get more details on the subject's activity.
If he refuses to give it to you then start thinking badly.
This is more frequent than it seems.
Although today it is much simpler to verify, the number of braggers who fill their mouths with "I am an entrepreneur" is incredible: the more they repeat it, the more you have to be careful.
Another worrying sign is the absence of the VAT number on any company website.