Silver advice, please help! I bought this 5oz piece a year ago from modern coin mart. It has a brown or tarnished stain but did not before and it's been in the plastic in came in.

So here are the pics l
Again when I bought it was clean now it almost looks like it's starting to rust. Please leave a reply letting me know if it's fake or just something else. The pic doesn't total pick it up but u can pretty much see it! I only took it outta the plastic today when I saw this.