Does all silver...?

No.

Coin silver (90%) is also widely used.

Occasionally you may find .750 silver.

"German" silver is NOT silver.

Yes, fake silver, especially when plated, is often stamped for fraudulent reasons.

The same goes for anything gold and the various stampings; 14K, 18K,  .585, .750, .916, etc.

If you don't know what you're doing, buy from a reputable source.

No.  .925 is sterling silver, 92.5% pure.  .999 or .9999 is pure silver.

Certainly dishonest people will intentionally falsify items.

I've not gotten fake silver (something claiming to be sterling that's really silverplate, for instance) that was made in the US.

But I've gotten fake silver made in both Mexico and India. Not that all silver from these places is suspect--I've gotten the real thing from both, too--but that you need to check the seller's ratings and customer satisfaction before purchasing from them.

925 means 92.5% pure . Sterling. I doubt silver is valuable enough to fake, but I've  seen hundreds of fake gold chains and rings over the years.