What are the reasons for an "Authentic" card?

[freakhappy]

This seems like an easy question to answer, and it probably is. But I've seen quite a few "Authentic" slabbed cards that look pretty sharp and sell for a high dollar amount. Is it possible for people to send their cards in to a TPG and ask just to slab it for authentication and not designate a number to it? If so, why would they do this? Also, wouldn't this just hurt the sale of the item b/c one would think there was something wrong with it b/c there is nothing explaining the "A" on the slab?

Just seems like these are going for too much if they are altered in one way or another.

The list for the "A" designation (off the top of my head):
1. Trimmed
2. Recolored
3. Skinned or Rebacked
4. Too much card missing for a "1" grade.
5. Certain "off" sets like Jello, Post, Bazooka, etc.,

Here are a few examples of what I'm talking about:

http://www.ebay.com/itm/260919618221

http://www.ebay.com/itm/260919614600