I combined two of those certificates for a free day at Budget Car Rental At BOS.

When I got the bill, and noticed that they had charged me tax for rental rate, I told the agent that charging me Massachusetts state tax for something I didn't pay (the rental rate I got free) is illegal. (And it is!!!).

I demanded that she take it off. She called the manager and I spoke to him politely. He agreed. Tax was taken off (cut $20 of my rental).

However, aiport usage fee, convention tax (what ever is that?), LDW/CDW charges that you opt for applies.

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For FTalkers who are renting cars at BOS, there is a citgo station on the airport island. It's a little tricky to find, but it will save you a lot of $$$$ in refuelling costs.