OK, couple of important qualifications here.In the US you deduct what you have paid in Sales Taxes and things like VRT, Property Tax, etc from you income before you pay income tax.
First, you can only claim a deduction for state taxes if you are claiming itemised deductions, rather than the standard deduction. Only about 10% of taxpayers claim itemised deductions — either the standard deduction works out more generously for them, or it is not sufficiently less generous to make it worth their while to do the huge amount of record-keeping and paperwork that claiming itemised deductions apparently involves. The 10% who do claim are, broadly speaking, the richest 10%. So the deduction for state taxes is irrelevant to the situation of the great bulk of taxpayers.
Secondly, somewhat bizarrely, you can claim a deduction for the state sales taxes you paid, or for the state income tax you paid, but not both. Presumably, if you want to claim for the state sales taxes, you have to be able to vouch your claim with receipt for all your expenditure during the year, which must be an utter pain. My guess is that most people claim the state income tax, which is more easily vouched, unleess they live in a state that doesn't have a state income tax.
Thirdly, stamp duties and transfer taxes are not deductible (because they're capital in nature).
Fourthly, there is a monetary cap on the total deduction you can claim in respect of all state taxes.
No, there's a cap on the amount of the mortgage in respect of which interest will be deductible.You can also deduct all of your mortgage interest,
And, again, you can only claim this if you claim itemised deductions - not if you claim the standard deduction.