A dealer might say he is doing you a favor; instead of getting you to pay the one-time fees while closing the deal, he will let you pay them over the life of the lease. This way, if you agree, your $600 security deposit could be $1,200 by the end of the amortization, because he is slapping you with a huge interest rate.
How to avoid: try to make an effort and pay the small fees the first time…unless you don’t mind paying double.