I agree with "jrapo" on the funds: certified bank check or wire transfer, with funds confirmed by your bank, is best. Cash works too, but with the dollar amounts you're talking about here, that's probably impractical... I personally would even accept a personal check -- if the buyer is willing to allow time for the check to clear before taking possession of the vehicle. As "jrapo" also suggests, a bill-of-sale, signed by both parties (and perhaps even notarized), is also a good idea. It doesn't have to be anything elaborate; just a sheet of paper briefly detailing the vehicle and the agreed selling price.
Your insurance agent should be able to answer the question about coverage during a pre-sale test drive. I would think you'd be covered, either by your insurance or that of the potential buyer, but...? :dunno:
Within-state transactions are relatively straight-forward; as I recall, the People's Republic of Maryland requires a 'safety' inspection prior to the title transfer? Sometimes the seller will acquire that to entice potential buyers, but ultimately I believe it's the buyer's responsibility. Having never transferred a vehicle to/from another individual during the time I lived there, I can't recall if Maryland requires a notary to transfer the title...? :dunno: Perhaps the best thing to do is meet the buyer at a nearby MVA office and take care of everything right then and there...?
Out-of-state transactions can be more involved, depending on the state of origin and the state to which the vehicle is being transferred. Different states seem to have different paperwork expectations, so you'll have to handle that on a case-by-case basis. Perhaps the only thing you need to know is what the expectations of Maryland will be in order to smoothly transfer the title to another state (notarized title signed over to the buyer, etc.)...? I'd check with the MVA. Regardless, the out-of-state purchaser will need to obtain a temporary/transit plate (usually cardboard) and registration, issued by Maryland in his name; don't agree to let the buyer drive off with your plates under the promise he'll mail them back to you; as I recall, Maryland expects you to turn them back in if the plates are not transferred to your new vehicle.
In the case of either transaction, if you don't witness the transfer yourself (e.g., buyer insists on taking the vehicle back home before transferring it), most states offer a form or some way to notify the MVA that the vehicle has been sold. I would look into that, as the procedure varies from state to state. This is designed to protect the seller, in case the buyer does not submit the paperwork to transfer the vehicle like he's supposed to do. If the vehicle is involved in an accident (or worse yet, some sort of criminal activity), and it's still registered/titled to you, they come looking for you first with any issues...
I don't think you have any tax obligations, as the seller; at least not so far as the sales taxes go. That's the buyer's concern, and he'll typically pay those only in the state in which the vehicle is to be registered/titled.