I let them know how much money they owe at this point, and that an eviction will make it nearly impossible for them to rent from other landlords.Then I'd say that we'll let them out free and clear, without them owing any more money, if they agree to move by such and such date, and that they will forfeit their deposit, to cover some of what they owe. 

One of my best tenants owns a smoke shop :) It's in their lease that they can only smoke outside on the terrace (they're in FL) and any smells or evidence of smoking in the unit will forfeit their deposit.

I don't how it works in other states, but here in Texas the cancellation fee actually protects the landlord.In our state the tenant does not forfeit the security deposit for breaking the lease.

Can a landlord request that the security deposit be forfeited if the renter requests to get out of the lease a month early? 

That would be a simple clause in the lease agreement he signed that stated he would forfeit some or all of his security deposit if the unit was not left in a cerntain condition.    

. #5--They signed a contract agreeing to forfeit the deposit which was NOT a security deposit, it was to hold the property till they could move in.

If they change their mind and fail to pay rent and take over on the lease start date, the holding deposit is forfeited and you put it back on the market.Holding deposits, security deposits, and first month of rent should always be paid in certified funds (money order, cashiers check) and never a personal check.

By that date, if Tenant decides not to rent the unit, then the holding deposit will be forfeited.  

Fourth, absolutely they will forfeit their deposit.

But, it appears this tenant is even willing to forfeit a few days rent.Believe me, if this tenant moves out as promised, and didn't leave the place trashed, you have a fantastic ex-tenant experience here.