car sales & sales tax contract question

I made an out of state purchase of a used automobile, had it shipped here to my residence in Fl. My intentions were to resell the car here and try to make a profit. After receiving the vehicle, I decided to trade the vehicle in due to the fact that it needed major $$ done in repairs. I had the vehicle, title, and related documents in my possession for a total of about 8 days. I traded the vehicle in at a local dealership for a new vehicle, and at that time I signed over the title to them, and explained to them why the vehicle was not in my name. They had no mention of any problems at that time, they even had a couple of different finance people review the documents during the sale / transaction.

I assumed at that time that if any taxes were due, that they would include them in with the total sale. Well, one week later they contact me saying that I need to come in and pay the sales tax on my trade in, after all paper work and contracts have been signed.

I went back at their request, and asked them what I needed to do. I was assuming that they wanted me to register my trade in vehicle in my name, pay the taxes due, and then sign it over to them again. They told me no, that the vehicle already sold, and that they would take care of it, and all I had to do is write them a check for the taxes due.


So my question here is, is this legal, can they do this? Or are they trying to pull one over on me, and extort money from me.