In my opinion this is a fake. The makers mark looks laser etched, not acid etched as I should be. The blade and makers mark look brand new, but there is no proper crossgaining. The cross guard seems to me stamped with a letter. If it is an SS dagger then the cross guard should be stamped with a numeral, if it is early vintage which this one is pretending to be.

For the sake of education, could you please post photos of the SS rune button, and a few more of the scabbard and hilt.

Others on this forum who have far greater knowledge than I will hopefully make some comments soon, but get prepared to take this thing back and get your money back. How much did the seller ask for it?