Two things to notice:
1. The seller admits in the description that the signature at the bottom of the letter isn't Anson's, but there is another on the back that might be?
2. This is the same seller that has the Delanhanty auto up for sale, which I do not believe to be genuine. Discussed in this thread:
http://net54baseball.com/showthread.php?t=164246
Just sayin