If the names are notarized, you should still be able to register the car. If they are not, you may be in trouble. What I would do is to go to an auto title transfer company. There are several around the state. They are usually inexpensive (less than $30 or so for their services) and can get you in and out quickly.
If you can't transfer the title, you will have no choice but to get the required documents or rescind the sale. Suing the seller will likely be very difficult, as you are across state lines. You may have to go to Florida to sue him (or at least to collect).
In general, I think it is a bad idea to buy vehicles from ebay. I always want to know that I am dealing with a local resident or company that I can sue locally if I need to.
