Somebody is going to be unhappy about this coin. The seller is calling it an 1899 Morgan when it is actually an 1899-O Morgan......big difference. http://cgi.ebay.com/1899-Morgan-Silver-Dollar_W0QQitemZ190122920744QQihZ009QQcategoryZ39466QQrdZ1QQcmdZViewItem
I agree that it is not the right coin but I wouldn't fault the seller on this one. He probably knows nothing about coins as his father left him them and the date is accurate. He probably doesn't know about mintmarks and he has posted a lot of pictures which clearly show the O. I just don't think the seller is trying to be deceiving on this one. To answer your question about the diffrence between a 1899 and a 1899-O: about $72 at VF-20 and up to around $400 at Ms-64
The 1899 P is a low mintage of 330,846 the 1899 O is 12,290,000 Value as an AU= 1899 P= $275 the 1899 O= $24.50 If the buyer really knew what he was doing, then he should have been more alert, if he was trying to get a buy, he should have checked the pictures. They are very clear, esp the mintmark. Sellers often do not know what they are really selling, and I don't think that he (the seller) was being devious.