Car, boat or TT my approach is always the same, when I find one I am interested in, I tell the salesman. “The price you quote is the number I write on the check; and I only bring one check!”
I make it abundantly clear that the price we agree on includes everything, taxes, prep, fees, lunch money for his kids or whatever. I write it down, I leave with the product.
It may not reduce the price but it does eliminate a lot of hidden last minute costs.
Take your time, do not be afraid to walk away from any deal. Think about it over night. Buying a high ticket item is not a race.
Do not obsess over whether you got the absolutely, cannot beat it, best deal. What is important is you got what you want at the price you want.
There are a lot of after sales cost. Insurance, license plates, roadside assistance etc. check these costs out before you buy.
Good Luck
