Credits are required?

From TaxAlmanac

As a newbie, I hope everyone will bear with what might be considered "naive" and rather generalized questions. A preparer of some extended experience made a comment to me the other day that I would like to check on. The statement was that as professional preparers, we are REQUIRED to file our client's returns with ALL credits that they are entitled to. I had never heard that before. The issue came up because the particular credit in question was worth less than the cost of preparing the form! So my question is three fold: 1) Is a taxpayer REQUIRED to take a credit, or can they elect to decline the credit if they feel it is to their benefit for some reason? 2) If they ELECT to decline the credit in one year, can they file an amended return later to claim the credit? And 3) As professional preparers, are we REQUIRED by law to file a client's return with credits that they would rather decline or could that merely be a "policy" of the firm? Your help and comments would be greatly appreciated!