Why aren't hallmarks always used?

[Zuzu]

Just curious to hear people's thoughts!

I'm purchasing a stunning Emilia Castillo piece online, but before I made the decision I was a bit suspicious of the hallmarks. She's a contemporary designer, yet there was no eagle or T-mark on what was supposedly a solid sterling piece - just her name (though not her usual mark) and '925 MEXICO STERLING', which I'm sure I don't need to tell you looked very wrong!

Thankfully I was able to contact Ms Castillo and she confirmed that the piece was indeed hers...but my question is, why aren't hallmarks always used? It's hard enough to know what's fake and what's not as it is, LOL.
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