Yes, I agree things will drive you crazy.  Like this energy credit.

The manufacturers certificate is like the gold standard here.  But the people who write this stuff do not live in the real world.  In theory, just have the certificate and you are done.  But the reality, at least with my clients and those of the preparers I network with, is that no one has the manufacturers certificate.  No one.  

I have asked clients to contact the seller to get the certificate and then after calling, they come back to me with a response of "We don't have a certificate but it qualifies" or the best one "You don't need a certificate".

In the case of a furnace, ac, or hot water heater, one can sometimes be found by doing some digging at the manufacturers website.  I usually don't even try on those items but rather I get the make and model and see if it meets the various qualification criteria for the item.

But doors and windows are another animal.  Who keeps the stickers?  Who knew to keep the stickers?  Today I got a receipt for a window installer saying 5 Marvin windows were installed. Client says they are energy efficient and swears salesmen said they qualify.  A little more digging resulted in a name , Elevate Casement, and a model 250.  Yet, from searching the product listing of qualifying items you can find through the links that Lisa provided above, there are pages upon pages of Marvin 250 windows.

The client doesn't know.  The salesmen usually say anything to make a sale.  The client thinks I have a cancelled check and new windows and that is good enough.

Maybe it will be better in a couple years when the client is to be provided some kind of identifying number for purposes of the credit.  But until that happens, I seem to be spending a lot of time chasing something that usually doesn't turn out too well in terms of qualifying.