Why big gap between web estimator and mechanic quote? why they keep alternator?

You were hosed, lose that mechanic/shop.

What did he bill you another 1.5 hours for? Didn't he show you an estimate before the work was completed. The reason he kept the alternator is because he has to return it as a core to the place he bought the new alternator from. Keeping parts for cores is a common practice, but he should be able to show you your old part to at least inspect. I still don't understand how he bumped the hours up to 3 after he quoted you 1.5 hours. Please explain more.

THE MECH NEEDS A CORE IF ITS R/B BUT NEW ALT HAVE NO CORE VALUE. SOUNDS LIKE MAYBE HE WANTS IT OR HE SOLD U A REBUILT AS NEW. THAT WOULD BE WRONG. THE LABOR SHOULD BE AROUND 1.5 HRS WITH DIAG FEE. YOUR BILL SHOULD BE APPROX 285.00 PARTS AND LABOR.SOUNDS LIKE YOU NEED A NEW MECH THAT IS HONEST