Laws vary by state, but generally speaking, if you (or the person taking the car for a test drive) gets pulled over for no tags, you're most likely going to get a ticket. Now once you write a bill of sale, things will be different for the person buying the car.
I've sold about 10 cars in the past 8 years. Never once did I let the person taking it on a test drive go out on their own. I always rode along. I also never let them meet me at my house. Always someplace public. If you're selling a nicer car (good working condition, a model that will interest alot of people), chances are you're going to have multiple people calling to set up a time to come see it. Last vehicle I sold (6 months ago), I actually had three people show up at the same time. First one with cash in hand gets it. Never accept a check. Ask me why I say that.
Be sure that you set your price high enough that you are willing to negotiate. Gives them a little wiggle room and you'll still end up getting what you want for the vehicle. Makes them feel they got a good deal, too. Make sure you have your title with you. I forgot the title on one vehicle and had to mail it. Forgot to mail it to the people quickly and got a very angry phone call about a week later. Told 'em it was my bad and mailed it that day. Of course, as soon as they got the title, they called me back an appologized for being so rude. But that doesn't happen every time.
Just a few tips. Hope you get what you need for the car!