Hi -
the marks look authentic - the salver and engraving looks too young.
Assayer: Jaschinkov (Jaschenkov) Aleksandr I. 1797-1825
The other 2 (?) punches are unknown to me.
Here another punch same time period to compare:
If you have to ask - don´t buy!
Regards
Goldstein
source: PL, p. 178