tax credit

I did a search, and saw many people complaining they had problems getting their tax credits. Most of those were a couple years back. So here:

1. Is IRS still denying credits when everything is in order and causing hassle and anxiety?
2. Is federal credit limited to what your actual tax is (like if your tax is $5000, you can't get full $7500)?
3. Is there a way to find out if the federal credit has been claimed/redeemed on a particular car? There is a local seller (private) who says I can get the federal credit because he didn't claim it I would hate to be out of money and then have to drag him guy to court (or police).

Tax credit is only available to first buyer so used vehicles that have been titled do not qualify. I had no problems with claiming the credits on both the 2011 and 2015, but I filed for extensions so my taxes were filed in October both years. There were some issues early in 2012 (2011 taxes), but the IRS seemed to have their processing issues taken car of by the time I filed. The tax credit is limited by your total tax liability (not withholding) in the year you purchase the car with a maximum credit of $7,500.